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KOSPI Closes at 6,813 on Foreign Net Buying of ₩3.72tn; Aftermarket Softer — Korea Market After-Hours, Aug 13, 2026

The KOSPI closed Thursday, August 13 (2026) at 6,813.34, up 3.56%, as foreign investors posted provisional net purchases of ₩3.72tn on the main board — the dominant buying force on the day against net selling by retail investors of ₩2.60tn and institutional net selling of ₩1.07tn (all figures provis

The Silmari
A daily data newsletter on the Korean stock market — silmari, ‘a clue: the loose end that unravels the knot’
⑤ After-Hours 18:002026.08.13 Thu · No. 11Sentiment gauge: neutral (composite score 0.752). 20-day realized volatility at 6.04 (94th percentile, 2026 regime expanding window); leverage ETF share of total turnover on Aug. 12 was 2.56% (73rd percentile). Credit balance and short-surge inputs are on a T+1/T+2 lag and are not yet available for today.
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).
01 · VerdictRegular session confirmed (2-source reconciliation)

verdict at evening

KOSPI Closes at 6,813 on Foreign Net PurchaseThe difference between the total value of shares bought and sold by a given investor group over a period; a positive number means that group bought more than it sold.The daily net buying figure for foreigners, institutions, and retail investors is the primary flow signal watched by Korean market participants to gauge directional conviction. of ₩3.72tn; Aftermarket Softer

The KOSPI closed Thursday, August 13 (2026) at 6,813.34, up 3.56%, as foreign investors posted provisional net purchases of ₩3.72tn on the main board — the dominant buying force on the day against net selling by retail investors of ₩2.60tn and institutional net selling of ₩1.07tn (all figures provisional as of 17:52 KST).The KOSDAQ closed at 861.37, up 0.29%, lagging the main board sharply — the morning call for KOSDAQ (+0.5~1.5%) overshot the actual outcome; the KOSPI call (+0.8~2.0%) undershot, with the index settling above the upper end of the projected range.

Key points
01KOSPI closed at 6,813.34 (+3.56%); KOSDAQ at 861.37 (+0.29%). Intraday range on the KOSPI was 147.5 points (2.19%), with the session high of 6,895.63 hit at 09:10 and the low of 6,748.13 at 15:03.
02Semiconductors led with a sector gain of 6.38%: Samsung Electro-Mechanics +12.58%, SK hynix +5.92%, Samsung Electronics +4.89%. Foreign net buying in Samsung Electronics alone was ₩154.3bn (provisional).
03Nextrade (Alternative Exchange)Korea’s first alternative trading system, operating pre-market, main-session, and after-market windows outside KRX; figures from NXT are separate from and additional to KRX volume.NXT aftermarket data provide the earliest available post-close read on whether the day’s price moves are holding or reversing among active participants. aftermarket snapshot (20-minute delay, as of 17:25 KST; NXT only, not KRX): 350 issues declining vs. 238 advancing; combined NXT turnover ₩1.797tn. Samsung Electronics and SK hynix each gave back a portion of the day’s gain in aftermarket trading.
04The morning KOSPI call (+0.8~2.0%) missed — actual was +3.56%, above the upper bound. The KOSDAQ call (+0.5~1.5%) also missed — actual was +0.29%, below the lower bound.
02 · NXTNXT intraday — 20-minute delay · as of 17:25 KST

Evening disclosures —Short 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 Tilts to Sellers — 350 Issues Down vs. 238 Up at the 17:25 Snapshot

In NXT (the alternative exchange, separate from KRX), the 20-minute delayed snapshot as of 17:25 KST showed 350 issues declining and 238 advancing out of 608 names, with combined NXT-only turnover of ₩179.7bn — these are NXT figures only and are not final confirmed data (confirmed daily totals are registered later in the evening).Among the top five NXT names by turnover, Samsung Electronics showed a gain of 3.13% and SK hynix +4.26% in the aftermarket snapshot, both running below their KRX closing-session gains of +4.89% and +5.92% respectively, while Samsung Electro-Mechanics was indicated at +10.56% vs. its KRX close of +12.58%.

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

Crash-Precursor Score Holds at 3 of 10; Volatility Percentile Elevated at 94th

Advance-Decline RatioThe ratio of advancing issues to declining issues in a market on a given day; a reading above 1.0 means more stocks rose than fell.ADR is used here as a market-breadth signal in the crash-precursor scoring model — a sustained extreme reading can flag either broad momentum or exhaustion.

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 2026-08-13

Evening Trading Principles

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

A 3.56% Up Day with Broad Lags in KOSDAQ and Aftermarket Retreat in Semis Warrants Watching the Spread

The collapse-precursor score is 3 out of 10 today, with the ADR signal (2 points) and the short-surge flag (1 point) as the active components; the two remaining inputs — panic-buying-on-down-days and sentiment-above-90 — are not triggered.Twenty-day realized volatility stands at the 94th percentile in the current 2026 regime (expanding window), which historically has been associated with wider intraday ranges — today’s 2.19% KOSPI high-low spread is consistent with that backdrop.In the current regime (2026), on the 32 Thursdays in the sample, foreign investors have been net buyers on only 28% of occasions; today’s provisional foreign net buying of ₩3.72tn is therefore directionally atypical for the day of the week — readers may find it useful to monitor whether the provisional figures are revised when confirmed data are registered later this evening. The judgment is each reader’s own.

Sources: Korea Exchange · NXT · 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.