KOSPI closes at 6,912.95 on August 21, 2026 — 683 stocks fell and the index still rose

The KOSPI rose 0.88%. On the same board, 683 stocks fell.

Both sentences describe August 21, 2026. The gap between them is the whole story of the day in Korean equities.

1. What was recorded

The first thing to notice is that the day started and finished in opposite directions. The KOSPI opened down 92.63 points, carrying over weakness in US equities and the pressure of rising Treasury yields. It then turned, reached 6,954.12 intraday, and settled at 6,912.95.

That is a 153-point swing from open to close. Modest next to the previous session's 381-point surge — but not modest inside the index.

2. Two stocks did the lifting

Both opened lower, tracking the overnight sell-off in US semiconductor shares. Both turned positive during the session, and the index turned with them.

That produced the day's defining number: 683 stocks on the main board fell while the index rose 0.88%.

An index does not count companies. It weights them by market value. Samsung Electronics and SK hynix are large enough in the KOSPI that gains of 3.87% and 2.31% outweighed declines almost everywhere else.

So the 0.88% does not mean the market rose. It means two chipmakers rose.

This extends the previous session. On August 20 SK hynix gained 12.73% and Samsung Electronics 9.49%, driving the KOSPI up 5.89% — covered on this page in "KOSPI closes at 6,852.58." Two days running, the same shareholder-return story concentrated in the same two names.

3. The KOSDAQ has no such heavyweight

The KOSDAQ fell 4.63% on combined selling by foreign and institutional investors. During the session, KOSDAQ 150 futures moved past the trigger threshold and set off the fourteenth sell-side sidecar of the year.

The list of decliners explains why.

Secondary batteries, chip equipment, robotics, biotech. What they share is that their profits lie ahead of them, not in the present.

Prices for such companies are set by converting distant future profits into a value today. The conversion uses a discount rate, and the floor under that discount rate is the long-term government bond yield. When yields rise, the same future profit is worth less now — and the further out it sits, the more it loses.

On August 21 the US 30-year Treasury yield climbed back toward 5.2%, undoing a one-day calm that the Treasury's expanded buyback programme had produced. The pressure hit the KOSDAQ's growth names before it reached the KOSPI's chip giants.

4. Every investor group changed sides

Set against the previous day, the shape inverts.

Foreign investors, who bought a net 2.299tn won on August 20, turned to a net sale of 170.8bn won. Institutions, who sold that day, bought. The sides swapped, but the size collapsed — August 21's flows are less than a tenth of the previous day's.

Retail investors sold for a second straight session. Having bought 5.64tn won on August 19, they sold 2.655tn won on August 20 and 1.166tn won on August 21 — roughly 3.8tn won returned within three sessions. Whether they profited cannot be calculated from public data, since neither the average purchase price nor the average sale price is published.

5. The won strengthened for a second day

The dollar-won rate fell 6.1 won to 1,386.5, after a 5.1-won decline on August 20.

But this time the direction does not line up. On August 20 foreigners bought 2.299tn won of Korean shares and the won strengthened — demand for won, stronger won, a clean explanation. On August 21 foreigners sold and the won strengthened anyway.

This page recorded the same mismatch on August 19, when foreigners sold 4tn won and the won still gained. Two of three sessions breaking the expected relationship suggests that whatever moved the currency this week was not equity flows. What it was, this page has not established.

6. What is unresolved

• 683 decliners — a single outlet's count, not checked against exchange data. The structure it describes, though, is reported consistently across closing wraps.
• Alteogen — one outlet printed 5.74% without a sign. Excluded from the table.
• Fourteenth sidecar — as reported; not re-verified against exchange records.
• The currency mismatch — two of three sessions moved against equity flows. No cause identified.
• What to watch next — Samsung Electronics' board is expected to fix the size of its shareholder-return package in August. That expectation is what lifted the index two days running, so the day the actual figure arrives could move it the other way. The structure of the package is covered in "Samsung's 100 trillion won shareholder return" and "What a special dividend is."