The Silmari

A daily data newsletter on the Korean stock market — silmari, ‘a clue: the loose end that unravels the knot’

⑤ After-Hours 18:002026.08.19 Wed · No. 16Sentiment gauge: Anxiety — score 0.97; 20-day volatility at 5.91 (93rd pctile, 2026 regime) and leverage ETF share at 13.39% (97th pctile, 2026 regime); credit and short data lagged by T+1 / T+2.

⑤ After-Hours · published 18:00 KST · after the regular session · Note: flow figures are preliminary as published just after the close; the exchange’s confirmed figures appear in that day’s Final Edition (20:00 KST).

① Pre-Open07:30 ② Early Session10:00 ③ Midday12:00 ④ Closing16:00 ⑤ After-Hours18:00 ⑥ Final20:00

01 · VerdictRegular session confirmed (2-source reconciliation)

verdict at evening

KOSPI Closes Down 5.8% — Semiconductors Lead Broad Selloff

The KOSPI closed Wednesday, August 19 (2026) at 6,471.17, down 5.8%, as a sharp selloff in semiconductor heavyweights — SK hynix off 9.75% and Samsung Electronics off 7.82% — drove the broader market through its session low of 6,400.81 hit at 09:17 before a partial recovery stalled well below the day’s high of 6,614.39.The KOSDAQ closed at 824.46, down 1.17%, with its intraday range spanning 804.02 to 840.50; the divergence in magnitude between the two indices reflected a rotation away from large-cap chip names toward smaller-cap defensive and biotech issues, amid a backdrop of U.S. long-bond yields spiking — the 30-year Treasury yield topped 5.33% overnight — alongside Middle East tensions and a Nikkei 225 that slid 3.16% to 65,326.42.

Key points

01KOSPI closed at 6,471.17 (−5.8%); intraday range 213.58 pts (3.34% high-to-low). Foreign investors were net sellers of ₩3,485.1bn on KOSPI today (provisional, collected 17:52).

02Semiconductor sector led losses: SK hynix −9.75%, Samsung Electronics −7.82%, SK Square −11.54%. Non-arbitrage program selling on KOSPI reached a net −₩3,371.7bn today, compared with −₩1,088.5bn on August 18 (2026).

03Today’s morning call (P1: KOSPI −1.5% to −3.0%; P2: KOSDAQ −2.0% to −3.5%) both missed — the KOSPI fell far beyond the forecast band at −5.8%, while the KOSDAQ fell less than projected at −1.17%.

04The sentiment gauge stands at stage “Anxiety” (score 0.97). Confirmed inputs: 20-day volatility 5.91 (93rd percentile, 2026 expanding window); leverage ETF share 13.39% (97th percentile). Credit balance and margin data carry an Aug 18 (2026) timestamp (T+1 lag); short-surge data carries an Aug 13 (2026) timestamp (T+2 lag).

02 · NXTNXT (Nextrade Alternative Exchange)Korea’s alternative trading system, separate from the KRX main board, operating pre-market, main, and after-hours sessions; its prices and volumes are distinct from KRX figures.After-hours NXT price moves can signal sentiment shifts before the next KRX open, but figures carry a 20-minute delay and are not final until the evening settlement report.NXT intraday — 20-minute delay · as of 17:25 KST

Evening disclosures —Short sellingShort sellingSelling borrowed shares first, betting the price will fall.A rising balance means more money is betting on a decline.balance

A window on whether the regular session’s move carried into the evening alternative venue

NXT After-Hours: SK hynix Partially Rebounds to ₩1,640,000 While Broader Tape Stays Skewed 459–133 Down

As of the 20-minute-delayed snapshot (reference time: 17:25, August 19 (2026)), NXT — the alternative exchange, separate from KRX main session — showed 459 decliners against 133 advancers across 608 issues, with aggregate turnover of ₩19,323.9bn; these are NXT-only figures and do not represent KRX main-session activity.Among the top five names by NXT turnover, SK hynix quoted at ₩1,640,000 (−1.32% vs. the NXT reference price) on ₩7,517.5bn of NXT volume, while Samsung Electronics quoted at ₩259,000 (−3.54%) on ₩4,900.2bn; these after-hours readings are unconfirmed provisional figures — final NXT session data will be published in the evening nxt_market release.

03 · Gap risksRisk → same condition in the past → outcome distribution

Tomorrow morninggap risks 4names

A window naming in advance what could shake tomorrow’s opening price

Overnight Gap Watch: S&P 500 Futures −0.37%, Nasdaq 100 Futures −1.12% as U.S. Long Yields Stay Elevated

ADRAdvance-Decline RatioThe ratio of advancing issues to declining issues in a market on a given day; a reading well below 1.0 signals broad-based weakness rather than concentration in a few stocks.Today’s crash-precursor score includes an active ADR signal, indicating that selling pressure was distributed across the market rather than confined to index heavyweights.

Warning score total: 3

signal 2 points

Short-interest surge

Warning score total: 3

signal 1 point

Selling acceleration

Warning score total: 3

signal 0 points

Sentiment 90+

Warning score total: 3

signal 0 points

05 · Principleas of 17:53 KST on 2026-08-19

Evening Trading Principles

A window recording the trading principles to hold to on the evening of a crash day

Crash-Precursor Score at 3 / 4 — Elevated But Below Full-Signal Threshold

Today’s crash-precursor score stands at 3 out of 4, with the ADR signal and the short-surge signal both active; the sell-acceleration and sentiment-90+ components are not triggered.When multiple signals overlap on a single session — as is the case today with U.S. long-rate pressure, a Nikkei drop of 3.16%, and a KOSPI decline of 5.8% — standard risk-management practice focuses on position-sizing relative to realized volatility rather than attributing the move to any single factor.The 2026-regime Wednesday base rate shows an average move of +0.92% with a 77% up-frequency across 31 sessions, so today’s outcome falls in the tail of that distribution; the sentiment gauge at Anxiety with a leverage ETF share at the 97th percentile suggests that overnight gap risk remains material until credit and short-balance data for today are confirmed (available T+1 and T+2, respectively).