Seoul — September 10, 2026. Published after the market close; prices for exchange-traded securities and indices are official closing values, while currency quotes are indicative market snapshots.
The 30-second version
- KOSPI slipped 0.25% to 7,033.92, sinking as low as 6,898.45 intraday — a 174-point swing — before defending the 7,000 line into the close.
- Foreign investors sold a net 2.49 trillion won (about $1.9 billion) of KOSPI shares, and program trading was a net seller of 2.54 trillion won, on futures-and-options expiry day.
- KOSDAQ went the other way, up 0.79% to 836.92, powered by 1.35 trillion won (about $1.0 billion) of institutional buying.
- Brent crude (November contract) spiked to $101.21 on renewed US-Iran hostilities — its first move above $100 since July 23 — lifting refiners and energy names.
- US PPI is due today and CPI tomorrow; futures markets price a 92% chance the Fed holds rates in September.
A stress test the day after a milestone
Yesterday, KOSPI closed above 7,000 for the first time in 33 trading sessions, finishing at 7,051.64 (+1.40%). Today was the stress test. September 10 was Korea’s quadruple witching day — the simultaneous expiry of stock-index futures and options plus single-stock futures and options. On expiry days, large arbitrage positions built up over the quarter get unwound at once, which can send waves of mechanical buying or selling through the market regardless of fundamentals. Think of it as a scheduled traffic jam: everyone knows it is coming, but the road still clogs.
Today the jam broke to the downside. Foreign investors, sitting on gains after yesterday’s rally, sold a net 2.49 trillion won (roughly $1.9 billion at today’s rate) of KOSPI shares, and program trading — automated, basket-level trades tied to those expiring derivatives — was a net seller of 2.54 trillion won. The index plunged from an intraday high of 7,072.79 to 6,898.45 before buyers stepped in and dragged it back above the line, closing at 7,033.92, down just 0.25%. Given the size of the selling, a quarter-percent loss counts as a successful defense, as Blockmedia’s closing recap put it.
Who sold, who bought — and why KOSDAQ diverged
The flow picture explains the split between the two markets. On KOSPI, retail investors bought a net 362.2 billion won and institutions a net 461.5 billion won (about $340 million), but that was nowhere near enough to absorb the foreign selling. On KOSDAQ, the smaller growth-stock market, institutions bought a massive net 1.35 trillion won — enough to overpower net selling of 1.07 trillion won (about $800 million) by foreigners and 268.7 billion won by retail, and push the index up 0.79% to 836.92.
That institutional bid showed up in specific names. Battery-materials maker EcoPro BM gained 3.31%. On the main board, value and dividend-flavored stocks outperformed: Samsung Electronics preferred shares rose 2.78% and Samsung Life added 1.98%, while property developers SK D&D and HDC posted strong gains.
Oil back above $100 redrew the sector map
The other big story arrived from the Middle East. Renewed US-Iran hostilities and worries about shipping disruptions through the Strait of Hormuz sent Brent crude (November contract) surging to $101.21 a barrel — the highest since May 22 and the first break above $100 since July 23. Refining and oil-linked names rallied hard: Korea Petroleum and Asia advanced, and smaller names including Fretee, Sempio and Sempio Foods surged toward Korea’s 30% daily upside price limit.
For most of the market, though, dearer oil is a cost, not a windfall — Korea imports nearly all of its crude. Add a rise in the US 10-year Treasury yield to 4.85% on inflation worries, which also supported the dollar, and the pressure on rate-sensitive and growth stocks was visible. Samsung Biologics fell 2.00%, LG Energy Solution 1.62%, and laser-equipment maker EO Technics 3.19%, while Samsung Electronics (-0.19%) and SK hynix (-0.16%) closed marginally lower. By sector, general services (-2.06%), pharmaceuticals (-1.92%), metals (-1.63%), financials (-1.56%) and medical/precision equipment (-1.28%) led the declines. Breadth was slightly negative — 419 advancers versus 443 decliners — meaning the average stock had a somewhat worse day than the headline index suggests. The won was marginally weaker, with USD/KRW quoted around 1,340 on September 10.
Today’s closing numbers
| Item | Close | Change | Note |
|---|---|---|---|
| KOSPI | 7,033.92 | -17.72 (-0.25%) | Intraday range 6,898.45–7,072.79 |
| KOSDAQ | 836.92 | +6.55 (+0.79%) | Institution-led rally |
| USD/KRW (Sep 10 snapshot) | ~1,340 | Marginally weaker | Continuous FX quote, no official close |
| KOSPI foreign net flow | -2.49 trillion won | ~-$1.9 billion | Drove the index lower |
| KOSDAQ institutional net flow | +1.35 trillion won | ~+$1.0 billion | Drove the index higher |
| Brent crude (Nov) | $101.21 | Spike | First $100+ since July 23 |
What to watch next
- US inflation data: PPI is due today (September 10) and CPI tomorrow (September 11). Per CME FedWatch, markets price a 92% probability the Fed holds at the September FOMC — the data will confirm or challenge that.
- Foreign flows: Whether today’s $1.9 billion of selling was one-off expiry mechanics or the start of sustained profit-taking after the 7,000 reclaim.
- Oil and Hormuz: Brent above $100 is a direct cost shock for import-dependent Korea; watch whether the geopolitical premium sticks.
- The 7,000 line itself: Reclaimed Wednesday, defended Thursday — a third straight close above it would strengthen the level.
FAQ
Why did the KOSPI fall on September 10, 2026?
A combination of quadruple witching day — the quarterly simultaneous expiry of futures and options, which triggered 2.54 trillion won of net program selling — and profit-taking by foreign investors, who sold a net 2.49 trillion won (about $1.9 billion) after Wednesday’s rally back above 7,000. The index still closed above 7,000 at 7,033.92, down only 0.25%.
What is quadruple witching (\”four witches day\”) in the Korean market?
It is the day when stock-index futures, index options, single-stock futures and single-stock options all expire at once. Arbitrage positions tied to these contracts unwind together, producing large mechanical program trades and elevated volatility — exactly the 174-point intraday swing seen today, per EBN’s market data desk.
Why did KOSDAQ rise while KOSPI fell?
Flows, not fundamentals. Institutions bought a net 1.35 trillion won of KOSDAQ shares — enough to absorb selling from both foreigners and retail — while KOSPI faced foreign and program selling that domestic buyers could only partially offset.
Which Korean stocks benefited from oil above $100?
Refining and oil-linked names such as Korea Petroleum and Asia rallied, with smaller names like Fretee, Sempio and Sempio Foods surging toward the 30% daily limit. Most of the broader market treats expensive crude as a cost headwind, since Korea imports its oil.
Disclaimer: This is an information and analysis publication, not investment advice. See our Methodology for data sources, standards, and our corrections policy.
Also on Seoul Closing Bell
A companion piece on the same session, written from a different angle: KOSPI Witching Day: Foreign Selling Was Program Flow, Not Panic.