The Silmari

A daily data letter on the Korean stock market — silmari, ‘the thread-end that unties the knot’

◈ Weekend — Monday Preview 20:002026.08.23 Sun · No. 20Sentiment: Neutral — as of Friday (08.21) close

◈ Weekend — Monday Preview · published 20:00 KST · ahead of Monday’s open

1 Pre-open07:30 2 Early10:00 3 Midday12:00 4 Close16:00 5 After18:00 6 Final20:00 KO

◈ Week in reviewSat 12:00 ◈ Monday setupSun 20:00 To the daily →KO

01 · Verdict◈ Weekend — Monday Preview · published 20:00 KST · ahead of Monday’s open

Five-minute brief

The KOSPI swung from a crash to a rally within one week. The KOSDAQ fell alone and closed the week broken.

KOSPI 6,912.95 −0.93% · KOSDAQ 801.94 −7.25% for the week. Monday turns on whether foreigners come back.

02 · Why18–21 Aug · Friday on Wall Street

What happened last week

1last weekThe index went nowhere but travelled a long way to get there. The KOSPI fell −5.80% on Wednesday, recovered +5.89% the next day, and closed Friday at +0.88%. For the week that is −0.93%, yet the high-to-low span was 12.75% — the 10th widest of 34 weeks this year. Twenty-day volatility on the KOSPI at 5.82 sits in the top 5% of the past year (as of 21 Aug). Foreigners and institutions did the selling: ₩3.47tn sold by foreigners on Wednesday alone, then ₩1.71tn bought back on Thursday. Ranges this wide argue for a wide Monday band.

2KOSDAQThe two boards split. The KOSDAQ lost −7.25% on the week, 31st of 33 weeks this year, and −4.63% on Friday alone — a bottom-5% move for the past year (as of 21 Aug). The KOSPI rose +0.88% that same Friday. On the week foreigners sold ₩1.85tn and institutions ₩2.27tn, while retail absorbed ₩1.94tn. The two indices usually move together; this week they did not. Whether the money that left the KOSDAQ moved to the KOSPI or left the market entirely is not something this data settles.

3Fri nightWall Street closed higher on Friday. The Dow rose +0.98%, the Nasdaq and S&P 500 +0.43% each, while the Philadelphia Semiconductor Index (SOX) went the other way at −0.51% (as of 21 Aug). The US 10-year yield at 4.74% is in the top 1% of the past year, near a one-year high. EWY, the US-listed Korea ETF, barely moved at +0.10%. The dollar index was flat at −0.10% and the won closed Seoul Friday at 1,388.0, −0.49%. Indices up but chips down, with yields at the top of their range — not yet a clean green light for Seoul on Monday.

03 · NumbersFriday’s close, 1-year percentile

Three numbers

US 10-year

4.74%

Top 1% of the past year — near a one-year high (as of 21 Aug). That is, among the highest 1% of sessions in twelve months With yields here, expensive growth names take the first hit.

KOSPI 20-day volatility

5.82

Top 5% of the past year — among the most volatile stretches (as of 21 Aug) The wider the swings, the wider Monday’s band has to be.

KRW per USD

1,383.9

Bottom 1% of the past 252 sessions — the won near its strongest in a year. ★Friday offshore close Seoul’s FX market is closed at the weekend, so this is the Friday offshore print.

03b · Chart

This week’s daily moves

KOSPI daily moves this week — each bar is labeled at its end.

Source: Korea Exchange

04 · Pattern

Pattern from the engine

In 2026 there have been 120 cases of a stock’s short interest more than doubling in five sessions. Five days later the stock was lower 49% of the time, average move −0.15% (ordinary-day average +2.67%). As of 18 Aug there are six such names — SK hynix 5.0×, Kumho E&C 3.8×, Ananti 3.3×, Halla Cast 2.4×, Samwha Capacitor 2.2×, Hana Micron 2.2×. Multiple and level are different things: the multiple says how fast short interest grew, the level says how much of the float is short. SK hynix grew fastest at 5.0× but its level is only 0.07%, while Samwha Capacitor at 2.2× carries 5.30% — the heaviest of the six. Read the two together. This is a 2026 sample measured five days out, not a rule for any single Monday.

05b · Chart

Weekly flows by investor

Four investor groups × weekday — net buying. Bars run left and right of the zero line.

Source: Korea Exchange

06 · Call29 Mondays in 2026

Monday’s call

KOSPI

avg −0.46% · avg range 3.43%

Direction59% up (n=29)

Foreigners

Monday avg ₩1.25tn net sell

Direction76% sell (n=29)

Basis · scoringThis is the record of 29 Mondays in 2026. The average is −0.46% but 59% of them closed higher — a handful of large declines drag the average down, while the ordinary Monday leaned slightly positive. The obstacle is foreign flow: in the same sample foreigners sold on 76% of Mondays, and last week they sold ₩1.85tn on the week. Scoring starts provisionally with Monday’s editions and is confirmed in the 20:00 edition. Every figure here comes from the 2026 Monday sample; none of it is a forecast for this particular Monday.

07 · Watch

Two things to watch

1Do foreigners come back? They sold on 76% of the 29 Mondays this year and sold again last week — but ₩3.47tn of Wednesday selling flipped to ₩1.71tn of Thursday buying, so Monday is not settled in one direction. The first flow print on Monday morning decides the session.

2Does the KOSDAQ close the gap? It trailed the KOSPI by 6.32 pts on the week. The crash-precursor score stood at 3 on Friday (advance-decline 2, short-interest spike 1); it carries lagged filings and is recomputed Monday morning. If the two boards move together again, last week’s gap was a one-week affair.