Today’s Verdict
KOSPI Drops 1.55% as Bond Yields Surge and Institutions Sell ₩795bn
The KOSPI closed at 6,869.83 on Tuesday, August 18 (2026), down 1.55%, after opening near 7,131, briefly touching a session high of 7,216.62 in the first 40 minutes, then reversing through the rest of the session to a low of 6,788.78 at 15:08 before a mild recovery into the close.The KOSDAQ fell harder, closing at 834.20, down 3.52%, while both morning forecasts — KOSPI rise of +0.5~1.5% and KOSDAQ flat to +1.0% — missed in direction; multiple headwinds including a 30-year U.S. Treasury yield touching 5.31%, heavy program selling, and broad institutional liquidation all contributed, and the data do not support attributing the decline to any single cause.
| Index | Close | Today | 1 week ago 08/11 | 1 month ago 07/16 | 1 quarter ago 05/19 | 6 months ago 02/13 | 1 year ago 08/18 |
|---|---|---|---|---|---|---|---|
| KOSPI | 6,869.83 | −1.55% | +8.26% | +0.72% | −5.53% | +24.75% | +116.22% |
| KOSDAQ | 834.20 | −3.52% | −2.76% | +5.35% | −23.07% | −24.58% | +4.53% |
Did our calls hold?
A window grading the morning’s calls against what actually happened
Both morning calls missed: KOSPI predicted +0.5~1.5%, actual −1.55%; KOSDAQ predicted 0.0~+1.0%, actual −3.52%.
Both morning predictions missed on direction.P1 called KOSPI +0.5~+1.5% (basis: Philadelphia Semiconductor IndexA U.S. index tracking major semiconductor and semiconductor-equipment companies, widely used as a leading indicator for Korean chipmaker stocks.An overnight SOX gain was the primary basis for today’s morning forecast; the mismatch with the actual outcome illustrates the limits of a single-signal approach. +1.64% overnight, current-regime next-day average +2.15%); actual was −1.55%. P2 called KOSDAQ 0.0~+1.0%; actual was −3.52%. The overnight SOX lead was real, but was overwhelmed by a 30-year Treasury yield surge, heavy institutional selling, and program outflows that were not captured pre-open.
No additional predictions beyond KOSPI and KOSDAQ market-level calls were entered for today’s session.
The day’s path
A window retracing where the index travelled from open to close
KOSPI opened at 7,131.30, peaked at 7,216.62 by 09:39, then sold off continuously to a session low of 6,788.78 at 15:08 before a partial recovery to close at 6,869.83.
Who bought and who sold —4 investorgroups ×4periods
A window on how much foreign investors, retail investors, investment firms and pension funds each bought and sold
Retail investors absorbed ₩742.0bn on KOSPI as institutions sold ₩795.1bn, but the index still closed down 1.55% to 6,869.83.
| Investor group | Today | 1W 08.11~08.18 | 1M 07.16~08.18 | Quarter |
|---|---|---|---|---|
| Foreign investors | +₩91.4bn | +₩8.13tn | +₩1.61tn | −₩76.16tn |
| Retail investors | +₩742.0bn | −₩7.24tn | +₩281.7bn | +₩59.30tn |
| Pension funds | −₩80.6bn | −₩176.3bn | +₩765.4bn | −₩2.68tn |
| Investment firms | −₩669.1bn | −₩410.4bn | −₩3.41tn | +₩18.39tn |
Foreign investors were net buyers of ₩91.4bn on KOSPI today, extending a one-week net purchase streak to ₩8,129.2bn.In futures, foreigners were net buyers of 808 contracts on August 18 (2026), consistent in direction with their cash-market stance — the 2026 current-regime data show a same-day correlation of 0.517 between foreign futures flow and KOSPI, but that relationship did not prevent a −1.55% close when institutional cash selling was large.
Retail investors net bought ₩742.0bn on KOSPI today, absorbing a share of institutional supply.Over the past week retail has been a net seller of ₩7,242.9bn; today’s reversal to buying on a down day fits the pattern in the 2026 regime data where retail and foreign flows show a same-day correlation of −0.85 — meaning retail tends to buy when foreigners sell, and vice versa.
National Pension Service net sold ₩80.6bn on KOSPI today after net buying ₩765.4bn over the past month.Securities firms net sold ₩669.1bn today, bringing one-month institutional net selling to ₩3,412.2bn; non-arbitrage program selling of ₩1,088.5bn on KOSPI reflects the same directional pressure from financial intermediaries.
KOSDAQ investor-level flow data are not available from the current feed (the Naver fallback supports KOSPI only), so a direct comparison of KOSDAQ net-buying breakdown is not possible for today.What is observable: KOSDAQ’s −3.52% decline was more than double KOSPI’s −1.55%, consistent with smaller-cap markets absorbing greater pressure when broad risk appetite contracts.
Over the current quarter (May 18 – August 18, 2026), foreigners are net sellers of ₩76,163.9bn on KOSPI while retail investors are net buyers of ₩59,300.1bn.This quarter-to-date structural divergence — institutions and foreigners offloading, retail accumulating — has been the dominant flow regime of 2026 and today’s session replicated it on a single-day basis.
Silmari Fear Gauge — past and present
A window measuring market anxiety through volatility, margin lending and short selling
The sentiment gauge held at 0.64 (neutral) even as the KOSPI fell 1.55% — crash-precursor score sits at 3 of a possible 4.
The sentiment gauge scored 0.64 today, placing it in the neutral stage.Of the eight components, two were confirmed for today: realized volatility (vol20) at 5.8, which sits at the 93rd expanding percentile; and the retail-down-day net-buying rate (pbuy_down) at 0.0, at the 70th percentile. The no-trigger streak was zero (not applicable — today’s decline had identifiable concurrent macro events). Credit margin (as of August 14, 2026) was 5.6% and the short-surge reading (as of August 12, 2026) was 7.8 — both delayed one to two business days per exchange and association publication schedules.
The data do not provide a direct tabulation of how often the neutral stage (score 0.35–0.65) was followed by further declines or recoveries in the 2026 regime.What the crash-precursor score does say: today’s reading of 3 out of 4 was driven by Advance/Decline RatioThe ratio of rising stocks to falling stocks across an index; a reading below 1.0 signals broad-based selling.The ADR component contributed 2 of today’s 3-point crash-precursor score, reflecting the U.S. session ADR signal of July 28, 2026. (2) and short-surge (1), with sell-acceleration and 90+ sentiment both at zero. The ADR signal references the U.S. session of July 28 (2026) at −16.7%.
| Measure | Today’s value | Basis | Where today sits |
|---|---|---|---|
| Retail buying intensity on down days | 0.0 | Current regime (2026) percentile | 70(top 30%) |
| KOSPI 20-day realised volatility | 5.8 | Current regime (2026) percentile | 93(top 7%) |
| Consecutive no-trigger down days | 0.0 | Current regime (2026) percentile | 86(top 14%) |
Today was a triggered decline day: the no-trigger streak component scored zero because identifiable concurrent macro events were present — specifically a 30-year U.S. Treasury yield at a 19-year high (5.31%), oil prices rising over 2% on U.S.-Iran talks stalling, and overnight U.S. equity losses.The gauge methodology excludes such days from the no-trigger-streak component, which is reserved for cases where the market declines without an identifiable external catalyst.
Because today’s decline was accompanied by multiple concurrent macro triggers, the no-trigger-streak component (weight 0.09) scored zero and was marked “not applicable.”On days where the market falls with no identifiable trigger, that component rises — and historically those sequences, once they lengthen, have been associated with fragility rather than catalyst-driven corrections. Today does not add to any such streak.
The sentiment gauge synthesizes eight inputs: (1) five-day credit balance trend (weight 0.135), (2) margin loan ratio (0.18), (3) retail net-buying rate on down days (0.09), (4) short-sale surge index (0.18), (5) 20-day realized volatility (0.225), (6) no-trigger decline streak (0.09), and (7) single-stock leveraged ETF share of turnover (0.10); a news-fear keyword proximity score is tracked as an eighth reference but is not included in the composite due to archive limitations.
The judgement is yours.
Short sellingSelling borrowed shares first, betting the price will fall.A rising balance means more money is betting on a decline.balance — the pattern of surges
A window on the stocks whose short balance rose or fell, and what happened afterwards
Short-sale surge signals on SK hynix and Simtec Electronics remain in the data; the current-regime (2026) five-day forward average after such surges is −0.50% with a 51% down-probability.
The most recent short-sale surge events in the data involved SK hynix (surges logged August 10 and 11, 2026 at 7.8× and 12.1× respectively) and Simtec Electronics (surges August 7 and 10, 2026 at 3.7× and 2.8×).The current-regime (2026) base rate for the five-day forward return after a short-surge event (defined as short interest at least doubling in five days with a base position of 50,000+ shares) is −0.50% average across 111 events, with a 51% probability of a decline — modestly above the coin-flip baseline but not a strong directional signal on its own. For comparison, the 2025 transition-regime average was +1.35% (111 events, 45% down-probability), and the pre-2025 regime average was −0.11% (150 events, 57% down-probability).
Where the money moved —12sectors
A window on where money moved from and to, by sector
Sector-level performance data was not collected for Tuesday, August 18 (2026); individual stock moves show broad-based selling with Samsung Electro-Mechanics off 7.57% leading large-cap declines.
| Sector | Today | Flows | Relative (1w) | Leaders |
|---|---|---|---|---|
| Semiconductors | — | — | — | — |
| AI & Software | — | — | — | — |
| Power & Electrical | — | — | — | — |
| Electronics & Components | — | — | — | — |
| Autos | — | — | — | — |
| Defense & Aerospace | — | — | — | — |
| Shipbuilding & Shipping | — | — | — | — |
| Financials | — | — | — | — |
| Bio & Healthcare | — | — | — | — |
| Construction & Infrastructure | — | — | — | — |
| Energy & Chemicals | — | — | — | — |
| Consumer & Entertainment | — | — | — | — |
The stocks that moved the market — top by turnover10
A window on which investor groups backed the most heavily traded stocks
SK hynix topped KOSPI turnover at ₩8,773.3bn while closing up 1.03%, the sole gainer among the ten most-traded blue chips.
On KOSPI, SK hynix led turnover at ₩8,773.3bn and closed up 1.03%; Samsung Electronics was second at ₩6,616.9bn but fell 2.19%, and Samsung Electro-Mechanics ranked third at ₩1,625.5bn with the day’s sharpest large-cap loss at 7.57%.On KOSDAQ, Ingenium Therapeutics (Reg.S) dominated at ₩715.5bn with a 49.92% gain; Jusung Engineering was second at ₩423.0bn, closing up 0.84%.
| Stock | Close | Change | Turnover | Foreign investors | Institutions | Investment firms | Pension funds | Retail investors |
|---|---|---|---|---|---|---|---|---|
| SK hynix | ₩1,662,000 | +1.03% | ₩8.77tn | +₩790.9bn | −₩123.6bn | −₩281.5bn | +₩120.9bn | −₩646.3bn |
| Samsung Electronics | ₩268,500 | −2.19% | ₩6.62tn | +₩176.7bn | −₩247.6bn | −₩215.2bn | −₩28.4bn | +₩83.9bn |
| Samsung Electro-Mechanics | ₩1,440,000 | −7.57% | ₩1.63tn | −₩418.7bn | −₩168.7bn | −₩57.3bn | −₩60.0bn | +₩582.4bn |
| SK Square | ₩1,135,000 | −1.65% | ₩845.3bn | +₩49.7bn | −₩35.9bn | −₩10.3bn | −₩12.4bn | −₩10.0bn |
| Samsung Electronics (Pref.) | ₩188,300 | −3.73% | ₩842.5bn | −₩188.2bn | +₩7.9bn | +₩2.6bn | −₩8.7bn | +₩175.5bn |
| Hyundai Motor | ₩435,000 | −3.97% | ₩383.7bn | −₩82.0bn | +₩1.3bn | −₩2.9bn | +₩0.2bn | +₩80.3bn |
| LG Electronics | ₩208,000 | −3.26% | ₩329.2bn | −₩27.4bn | −₩12.9bn | −₩22.5bn | +₩7.6bn | +₩39.7bn |
| Samsung SDI | ₩488,000 | −5.43% | ₩243.2bn | −₩35.1bn | −₩8.7bn | −₩4.8bn | −₩0.5bn | +₩44.2bn |
| SK eternix | ₩58,500 | +0.34% | ₩230.9bn | −₩11.6bn | +₩11.1bn | +₩2.6bn | +₩2.6bn | −₩0.4bn |
| LG Innotek | ₩633,000 | −3.21% | ₩215.2bn | −₩52.3bn | −₩11.7bn | −₩13.9bn | −₩1.0bn | +₩65.8bn |
Gainers5· Decliners5 — KOSPI & KOSDAQ
A window on the biggest gainers and decliners, and the reasons behind them
Market breadth data for August 18 (2026) could not be collected from the individual-stock price feed; the advance/decline count is not available for this session.
The advance/decline count for today’s session is not available — the individual-stock price feed returned a collection error for both KOSPI and KOSDAQ breadth on August 18 (2026); the most recent confirmed breadth data are from August 14 (2026) when KOSPI showed 677 advancers versus 204 decliners (ADR 3.32).From the ranked movers, KOSPI decliners in the data include names falling 6–13%, with gainers mostly in small shipping and food-service names (Heungah Shipping +12.90%, DabomKorea +21.84%); on KOSDAQ, the pattern was similarly bifurcated, with Ingenium Therapeutics surging while Aora fell 26.16% and Bonne fell 23.22%.
The SilmariDecouplingWhen two markets that used to move together break apart and move separately.The wider the gap, the less any single index can tell you about the market.Gauge
A window on the pattern in the KOSPI–KOSDAQ decoupling
KOSDAQ closed at 834.20, down 3.52% — more than double KOSPI’s loss — with the intraday range spanning 44.62 points (5.39% of the session open).
The KOSDAQ closed at 834.20, down 3.52% — a gap of 1.97 percentage points wider than the KOSPI’s 1.55% decline.The KOSDAQ’s intraday high of 872.59 was reached at 10:15 — roughly 35 minutes after KOSPI’s peak — and its low of 827.97 also arrived at 15:08 in tandem with KOSPI; the wider percentage loss reflects the heavier weighting of growth and small-cap names in the index relative to the KOSPI’s large-cap structure, particularly on a day when risk appetite contracted.
Semiconductors → defensives, and back — by regime
A window on the pattern in sector rotation — money circulating from one sector to another
The rotation base-rate dataset covers 118 prior defensive-flight episodes; whether today qualified as one cannot be confirmed without sector-level performance data.
| Regime | Reversion rate · sample |
|---|---|
| ① Old order (2018–24) | Average−0.84%· rose 45% of the time · 69 past cases |
| ② Transition (2025) | Average+1.70%· rose 71% of the time · 17 past cases |
| ③ Current regime (2026–) | Average+2.05%· Up 69% · 32 times previously |
A day when semiconductors (the average of SK hynix and Samsung Electronics) fall 2.0% or more while defensives (bio, food & beverage) outperform by 2.0%p or more = rotation (a flight)
The rotation definition requires semiconductor names (SK hynix and Samsung Electronics average) down at least 2.0 percentage points and defensive sectors (bio and food) outperforming by at least 2.0 percentage points on the same day.Today Samsung Electronics fell 2.19% while SK hynix rose 1.03% — a mixed semiconductor signal — and sector-level bio and food data were not collected, so a formal rotation classification cannot be made. The KOSDAQ decline of 3.52% argues against a clean defensive rotation.
The night makes the morning —American Depositary Receipt (ADR)A twin of a Korean stock, listed on a U.S. exchange.It prints overnight, showing how U.S. investors price Korean stocks before Seoul opens.crash detection
A window on how U.S.-listed Korean stocks moved overnight
The crash-precursor score printed 3 (ADR 2 + short-surge 1), with sell-acceleration and sentiment components at zero.
The crash-precursor score of 3 reflects ADR contributing 2 points (referenced to the July 28, 2026 U.S. session at −16.7%) and the short-surge component contributing 1 (based on the August 12, 2026 short-balance filing).The sell-acceleration component is scored from August 13–14, 2026 confirmed flow data and came in at zero today; the sentiment-90+ component (requiring the gauge to exceed the 90th expanding percentile) also scored zero at today’s level of 0.64. A score of 3 is the second step from the maximum of 4 — the data do not specify a historical hit rate for this score level, so no probability can be assigned here.
Tonight — the U.S. session about to open
U.S. equity futures point lower as the 30-year Treasury yield topped 5.31% and S&P 500 futures were off 0.69% at 05:00 KST.
Korea–U.S. mutual following — overnight grading
A window on which market followed which
Overnight S&P 500 futures fell 0.69% and Nasdaq 100 futures 0.81% as of 05:00 KST, preceding KOSPI’s 1.55% decline — direction aligned.
Overnight on August 17–18 (2026), S&P 500 futures fell 0.69% and Nasdaq 100 futures fell 0.81% before Korea’s open; the KOSPI then declined 1.55% — both directions aligned (negative following negative).The Nikkei 225 closed at 67,460.73, down 1.82% today, also in the same direction, adding a regional dimension to the pressure.
In the 2026 year-to-date sample of 139 trading days, Korea followed the U.S. (overnight SOX leading Korea the next day, same direction, |SOX| ≥ 0.5%) on 39 occasions; the U.S. followed Korea on 30; both moved together without a clear lead on 46 days; and neither followed the other on 24 days.Today’s configuration — U.S. futures negative, Korea negative — fits the Korea-follows-U.S. pattern, which has occurred in roughly 28% of 2026 sessions.
Overnight SOX ↔ same-day KOSPI in the same direction (|SOX| ≥ 0.5%) = Korea following · same-day KOSPI ↔ that night’s SOX in the same direction (|KOSPI| ≥ 0.5%) = the U.S. following
The won — the signal is the speed of the move, not its direction
A window on the pressure the won-dollar rate puts on foreign flows
The won/dollar rate stood at ₩1,410.40 per dollar with the yen cross at ₩883.29 per 100 yen as of the latest strip reading.
The won/dollar rate stood at ₩1,410.40 per dollar in the latest strip reading, with the dollar index (DXY) at 99.64, down 0.03% on the day.The yen cross was ₩883.29 per 100 yen; the Nikkei 225 fell 1.82% today and Nikkei CME futures were off 0.40% overnight, suggesting yen-side dynamics were not the dominant regional driver.
Rates — a weaker link than commonly assumed
A window on the burden rates and bonds place on equities
The 30-year U.S. Treasury yield crossed 5.31% overnight, a level not seen in 19 years per the event calendar, lifting the 10-year reference rate to 4.70%.
The 30-year U.S. Treasury yield breached 5.31% overnight — the event calendar notes this is a 19-year high — as oil prices rose over 2% on stalled U.S.-Iran negotiations, adding to fiscal-deficit concerns from the Nvidia/OpenAI data-center financing announcement.The 10-year U.S. Treasury yield stood at 4.70% as of August 14 (2026); the August 18 intraday reading is not separately confirmed in the strip data beyond the event calendar reference.
Reference — brokerages, Wall Street and the windows
A window collecting brokerage research and overseas news
No brokerage reports were published in today’s data — the research archive retrieves current filings only and no same-day reports were captured.
No brokerage reports were captured for today’s edition. The research archive (Naver Research) retrieves only currently available filings; reports dated August 18 (2026) were not collected at the time of data gathering and cannot be reconstructed after the fact.
15 of 28 calls correct (54%) — measured three trading days after publication.
The Wall Street Scoreboard tracks directional calls on Korean equities made by nine brokerages over a rolling three-session horizon; a call is scored as a hit when the predicted direction matches the actual KOSPI move at the stated timeframe. The current cumulative tally is 15 hits out of 28 calls (54% accuracy). Per-firm: Nomura 4/6, Goldman Sachs 3/5, Morgan Stanley 3/4, Citi 2/3, Bernstein 1/1, UBS 1/1, Macquarie 1/3, JP Morgan 0/3, Barclays 0/2.
Pre-market headlines from the event calendar relevant to today’s session included: the 30-year U.S. Treasury yield touching a 19-year high (03:45 KST); Brent crude back above $90 on U.S.-Iran talks stalling (04:50 KST); Nvidia backing $105bn in OpenAI Ohio data-center financing (06:22 KST); and Anthropic reporting a $65bn annualized revenue run rate as of July (06:26 KST). Post-close items — the domestic real-estate tax dispute and presidential remarks — arrived after the session and are noted here for completeness.
Individual stock commentary from brokerages is not available for August 18 (2026); readers should consult firm research portals directly for company-specific analysis.
Closing today, on to tomorrow
A window that closes today and hands over to tomorrow
Both calls missed badly: the SOX-led upside signal that formed the basis for the morning forecast was overridden by a combination of U.S. long-bond selling, a surge in the 30-year Treasury yield to 19-year highs, and heavy institutional net selling of ₩795.1bn — none of which were fully weighted in the pre-open model.The lesson is that a single strong overnight signal (SOX +1.64%) is insufficient when multiple macro headwinds — rising long-end yields, geopolitical oil-price pressure, and program-trading outflows of ₩1,070.3bn — are simultaneously active.