The Silmari

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

⑤ After-Hours 18:002026.08.20 Thu · No. 17Neutral — composite score 0.715; 20-day volatility at 6.05 (94th-percentile, confirmed); credit balance and short-sale residual inputs remain on reporting delay.

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 Surges +5.89% as Semis Lead — Morning Call Missed

The KOSPI closed Thursday, August 20 (2026) at 6,852.58, up 5.89%, reversing the prior session’s heavy loss as SK hynix (+12.73%) and Samsung Electronics (+9.49%) together accounted for ₩160.7bn of the day’s top turnover.The KOSDAQ ended at 840.89, up 1.99%; the morning call on the KOSPI was a miss — the model projected a decline of 0.5–2.5% but the index rallied sharply throughout the session, touching a session low of 6,600.09 at 09:08 before climbing to a session high of 6,904.55 at 13:14.

Key points

01KOSPI closed at 6,852.58 (+5.89%); session range 6,600.09–6,904.55, an intraday swing of 304.46 pts (4.61%). Morning call for a decline of 0.5–2.5% missed.

02Foreigners net bought ₩1,707.9bn in KOSPI cash on a provisional basis; retail investors net sold ₩2,271.3bn. In KOSPI futures, foreigners net sold 2,142 contracts while institutions net bought 3,204 contracts — current-session cash and futures flows diverged in direction.

03SK hynix (+12.73%, ₩9,109.6bn turnover) and Samsung Electronics (+9.49%, ₩6,960.7bn) led volume. Financials and energy names pulled back: KB Financial (−3.85%), Woori Financial (−5.82%), S-Oil (−5.94%), LS (−5.86%).

04The sentiment gauge sits at 0.715 (neutral stage). The 20-day volatility component stands at 6.05 (94th percentile, confirmed). Credit balance and short-sale residual figures carry a one-to-two-day reporting lag and have not yet been confirmed for today.

02 · NXTNXT (Nextrade)Korea’s alternative trading venue that operates extended pre-market and after-market sessions alongside the main KRX exchange.NXT data provide a real-time directional read on how participants price Korean equities outside standard KRX hours, though the figures are separate from and cannot be directly added to KRX main-market totals.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 Aftermarket Active: 385 advancers vs. 200 decliners, SK hynix and Samsung Electronics the top two by turnover

As of the 20-minute-delayed NXT snapshot (reference time: 17:25, Thursday, August 20 (2026)), 385 issues advanced and 200 declined across 608 names on the alternative exchange, with aggregate turnover of ₩169,407bn — these are NXT (alternative exchange) figures only, not KRX main-market data, and are not yet final.SK hynix led NXT by turnover at ₩56,941bn (+12.07%), followed by Samsung Electronics at ₩45,812bn (+9.09%); confirmed NXT session totals will be available in the final edition after the evening registration.

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 inputs are mixed: S&P 500 futures up +0.21%, but July FOMC minutes flagged rate-hike contingency and US national debt crossed $40tn

ADRAdvance-Decline Ratio (ADR)The ratio of advancing issues to declining issues in a market on a given day; a reading below 1.0 means more stocks fell than rose.ADR is one component of the crash-precursor score; a sustained low ADR (many more decliners than advancers) contributes to the composite risk signal.

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 17:55 KST on 2026-08-20

Evening Trading Principles

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

A +5.89% rebound day with a crash-precursor score of 3: track divergences between cash and futures, and between index breadth and sector moves

Today’s crash-precursor score stands at 3 (of which ADR contributes 2 and short-surge 1); on days when sharp recoveries follow heavy losses, the internal composition of breadth and flow data often carries more forward information than the headline index move alone.Today’s KOSPI cash showed foreign net buying of a provisional ₩1,707.9bn while KOSPI futures saw foreign net selling of 2,142 contracts — when cash and futures move in opposite directions among foreigners, the 2026-regime lag data suggest the futures position has historically carried a higher near-term signal weight.Non-program arbitrage buying contributed ₩12,719bn net on the KOSPI today, reversing the prior session’s heavy net selling of ₩33,721bn; participants monitoring overnight gap risk should note that program flows can shift direction rapidly and that today’s credit balance and volatility inputs remain on a one-to-two-day reporting delay.