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Wall Street selloff ripples into Seoul open — KOSDAQ gaps lower as defense and power stocks retreat — Korea Market Morning Session, Aug 21, 2026

The Silmari
A daily data newsletter on the Korean stock market — silmari, ‘a clue: the loose end that unravels the knot’
② Early Session 10:002026.08.21 Fri · No. 18Sentiment gauge: Neutral (composite score 0.581) — 20-day volatility at the 93rd percentile (value 5.97); leverage ETF share 8.78% at the 64th percentile; credit balance and short-surge readings are delayed (last confirmed Aug 19 and Aug 14 respectively); no-trigger streak = 0.
② Morning Session · published 10:00 KST · session in progress
01 · VerdictRegular session confirmed 15:30 KST

10:00verdict at this hour

Wall Street selloff ripples into Seoul open — KOSDAQ gaps lower as defense and power stocks retreat

The KOSPI opened at 6,759.95 on Friday, August 21 (2026), dipping below the prior close before recovering toward 6,910 by 09:48, then retreating; the KOSDAQ gapped down at 824.05 and ground lower through the opening hour, touching 807.05 by 09:52.The overnight backdrop included S&P 500 futures off 0.97%, Nasdaq 100 futures off 1.20%, and Nikkei 225 futures (CME, yen-denominated) down 1.18% as of 05:00 KST, alongside a U.S. 10-year Treasury yield that climbed 0.92% to 4.70% — multiple macro cross-currents were in play simultaneously.

Key points
01Morning call — split verdict (provisional): P1 (KOSPI up +0.3+1.5%) marked ✓ with an actual of +0.75% (confirmed close -0.93%per the day’s confirmed data — provisional intraday score; final verdict in the evening edition). P2 (KOSDAQ flat,-0.5+0.5%) marked ✗ with an actual of -4.05% at the time of scoring (confirmed close -3.74%). Both marks are provisional; final scoring publishes in the evening edition.
02Overnight macro: U.S. Treasuries re-extended their selloff — the 10-year yield rose 0.92% to 4.70% — while the S&P 500 fell 0.87% and the Nasdaq lost 1.00% on August 20 (2026). The Philadelphia Semiconductor Index (SOX)A U.S. equity index tracking roughly 30 semiconductor-design and -equipment companies, widely used as a real-time proxy for global chip-sector sentiment.Korean chip exporters such as SK hynix and Samsung Electronics have historically moved in tandem with SOX, making overnight SOX moves a standard input for Seoul open calls. semiconductor index gained 0.53%, providing a partial offset; the iShares MSCI South Korea ETF (EWY)A U.S.-listed exchange-traded fund tracking large- and mid-cap Korean equities; its after-hours price reflects how offshore investors are pricing Korean market risk overnight.Because EWY trades in New York while KRX is closed, its moves give a real-time foreign-investor signal that often sets the direction of the Seoul open gap. Korea ETF closed up 2.14% on August 20, reflecting the prior session’s strength.
03Sector divergence: Defense & aerospace fell 5.7% as a group, power & electric off 3.82%, and AI/software down 3.76% — all moving in the same direction simultaneously, making single-cause attribution unsuitable. Financials bucked the trend, edging up 0.06%, with KB Financial +1.06%, Shinhan Financial Group +1.48%, and Hana Financial Group +1.70%.
04Flow snapshot (provisional, collected 09:52 KST): On the KOSPI, foreigners net-bought ₩101.7bn and the National Pension Service net-bought ₩58.0bn, while retail investors net-sold ₩195.1bn and institutional investors as a whole net-sold ₩75.8bn. On the KOSDAQ, retail investors net-bought ₩231.0bn while foreigners net-sold ₩138.5bn. All figures are intraday provisional; confirmed data publishes this evening.
02 · SnapshotUntil 10:00 AM · Korea Investment & Securities 5-min index (highs/lows based on 5-min close)(may differ slightly from exchange official figures)

10:00Snapshot

A window that records the market at that hour, like a photograph

KOSPI opens with a ₩4.04 gap below prior close and recovers toward 6,910 by 09:48 before retreating; KOSDAQ presses lower through the first hour

KOSPI at 10:00Open6,759.95· High6,901.87(09:45) · Low6,767.34(09:05) · as of 10:006,829.95
KOSDAQ at 10:00Open824.05· High815.82(09:00) · Low801.04(10:00) · as of 10:00801.04
03 · Top 10 checkpointsKorea Investment & Securities minute bars · Until 10:00 AM

Top by trading value10— snapshot

A window on how the top trading-value names have moved up to this hour

SK hynix and Samsung Electronics drive KOSPI turnover to ₩2.22tn combined in the first hour; Kumho names and SK Securities dominate the active movers list

By 09:52 KST, SK hynix led KOSPI turnover at ₩1.30tn and Samsung Electronics followed at ₩918.2bn, together accounting for the bulk of activity; both stocks reached their intraday highs at 09:48, with SK hynix touching ₩1,771,000 and Samsung Electronics reaching ₩276,000.On the KOSDAQ, Ingenia Therapeutics (Reg.S) led turnover at ₩148.7bn, followed by Gido Industry at ₩87.8bn and Danal at ₩57.1bn; HPSP, Alteogen, and Jusung Engineering were also active, with Alteogen trading at ₩28.6bn and falling 5.15% from its open by the 09:52 snapshot.

Top 10 by trading value — prior close · open · gap · 10:00 snapshot (may have minor variance vs. exchange official)
StockPrior closeOpenOpening GapThe difference between the previous session’s closing price and today’s opening price; a gap down means the market opened below yesterday’s close without trading the levels in between.A gap signals information that arrived overnight — earnings, macro data, geopolitical news — and its size and subsequent fill pattern are early indicators of session tone.High (time)Last at 10:00ChangeLow (time)
Samsung Electronics271,000267,000−1.48%276,000 (09:48)272,500 (10:00)+0.55%266,000 (09:03)
SK hynix1,691,0001,675,000−0.95%1,773,000 (09:52)1,754,000 (10:00)+3.73%1,671,000 (09:01)
Samsung Electronics (Pref.)191,200190,100−0.58%207,500 (09:49)204,000 (10:00)+6.69%190,200 (09:01)
Samsung Electro-Mechanics1,396,0001,345,000−3.65%1,348,000 (09:11)1,326,000 (10:00)−5.01%1,321,000 (09:01)
SK Square1,123,0001,096,000−2.40%1,141,000 (09:48)1,118,000 (10:00)−0.45%1,079,000 (09:01)
Kumho E&C15,65015,650+0.00%18,200 (09:25)16,120 (10:00)+3.00%14,810 (09:02)
Kakao38,70038,150−1.42%38,650 (09:04)36,350 (10:00)36,100 (09:32)
Samsung Life Insurance296,989291,500−1.85%306,500 (09:52)298,000 (10:00)287,000 (09:01)
SK Securities2,8102,920+3.91%3,555 (09:05)3,220 (10:00)+14.59%3,000 (09:01)
Kumho Electric7,4608,000+7.24%9,690 (09:24)9,120 (10:00)+22.25%7,810 (09:02)

Among individual trajectories, Kumho Electric opened at ₩8,220, reached its session high of ₩9,690 at 09:24, then pulled back — a wide intraday range of ₩1,880 in under 25 minutes.SK Eternix moved in the opposite direction, opening at ₩54,100, peaking at ₩55,700 at the open, then sliding to an intraday low of ₩51,000 at 09:49 — a decline from open to low of ₩3,100; Doosan Enerbility similarly opened near its high of ₩77,900 at 09:00 and reached its low of ₩73,700 at 09:35.

04 · Up · DownReason labels: [News] confirmed · [Pattern] inferred

Gainers5· Decliners5— snapshot

A window on the biggest gainers and decliners, and the reasons behind them

Broad-based declines across 10 of 12 sectors; financials and select chipmakers hold positive ground as defense, power, and small-cap tech retreat

On the KOSPI, the advance side was narrow: Kumho Electric surged +28.95%, SK Securities +15.30%, and Kumho Construction +12.65% — all concentrated in names with company-specific catalysts rather than sector themes — while SK hynix added +1.42% and Samsung Electronics preferred shares gained +3.66%.The decline side was broader and heavier: Doosan Fuel Cell fell -10.46%, LIG Defense & Aerospace -8.64%, OCI Holdings -7.59%, SK Eternix -7.14%, and Hanwha Solutions -6.96%; on the KOSDAQ, Komico surged +27.52% but the decline list included SPG -7.54%, D&D Pharmatech -7.44%, Robotis -7.24%, and Gido Industry -7.22%.Physical-AI sub-themes reflected the broader pressure: robotics names tracked at -5.23% (n=2) and humanoid names at -5.04% (n=3), while autonomous driving slipped -1.62% (n=2); sector-level flow data for each group was not collected in this data run.

Gainers —5:00as measured at this hour
Komico * (KOSDAQ)+27.06%· turnover ₩43.8bn
Coocon (KOSDAQ)+23.17%· turnover ₩17.9bn
Uri Technology Investment * (KOSDAQ)+19.96%· turnover ₩137.7bn
IndiEF+18.26%· turnover ₩19.2bn
Galaxia Moneytree (KOSDAQ)+12.61%· turnover ₩85.5bn
Losers —5:00as measured at this hour
Gidosan Industries * (KOSDAQ)−34.58%· turnover ₩213.4bn
Alginomics * (KOSDAQ)−18.18%· turnover ₩24.4bn
Enchem (KOSDAQ)−15.98%· turnover ₩14.7bn
Ingenia Therapeutics (Reg.S) * (KOSDAQ)−13.97%· turnover ₩415.3bn
Gigavis (KOSDAQ)−13.40%· turnover ₩17.9bn
Historical contextSelection: turnover of ₩10bn or more · machine ranking by percentage change.
Sources: Korea Exchange · Nextrade (NXT) Alternative ExchangeSouth Korea’s second stock exchange, launched in 2025, which operates pre-market and after-market sessions beyond KRX hours; its pre-market price is a first signal of how participants are pricing stocks before the 09:00 KRX open.NXT pre-market turnover and price moves can front-run the KRX open gap, making NXT data a useful early-session directional indicator. · own measurements · regular session confirmed 15:30 KST · The Silmari editorial desk.
This edition organises and explains publicly available market data. It is not investment advice. Predictions and their scores are preserved without revision — the judgement is yours.