Seoul — September 11, 2026. Published after the market close. Index and individual stock prices are official exchange closing values; currency, oil, and bond-yield figures are quoted levels from continuously traded markets around the time of Korea’s close and the preceding overnight session.
The 30-second version
- The KOSPI closed at 6,909.91, down 1.76% (-124.01 points), after plunging as much as 3.29% intraday to 6,802.50 — losing the 7,000 level it had held above.
- The KOSDAQ fell 1.95% to 820.64. The won weakened, with the dollar quoted around 1,344 won (up about 0.4%) on safe-haven demand.
- Two overnight shocks did the damage: WTI crude surged above $100 a barrel on escalating US-Iran conflict, and the US 10-year Treasury yield spiked to around 4.95% overnight, with the 30-year at its highest in roughly 19 years.
- Foreign investors dumped about 2.46 trillion won (~$1.8 billion) of KOSPI shares and institutions sold another 1.64 trillion won (~$1.2 billion); retail investors bought roughly 2.43 trillion won of the dip.
- Semiconductors led the decline — Samsung Electronics fell as much as 4.09% — while shipbuilder HD Hyundai Heavy Industries (+5.6% to +6.3%) and bank stocks were the rare winners.
A 3% plunge at the open, then a partial rescue
Korean stocks opened in freefall. The KOSPI gapped down more than 3% at the bell, breaking below 7,000 and touching 6,802.50 — a 3.29% intraday loss — before dip-buying trimmed the damage to 1.76% by the close, according to Financial News. The KOSDAQ followed the same script, opening near 816.91 (down 2.39%) and clawing back a little ground to finish at 820.64.
The trigger was a double dose of bad macro news from overnight. First, the US-Iran conflict escalated, with tanker attacks near the Strait of Hormuz raising fears of a genuine supply disruption. WTI crude (October contract) surged above $100 a barrel during the overnight session and Brent (November) was quoted 4.1% higher at $105.38, per E-Today. Second, US Treasury yields spiked overnight — the 10-year to around 4.95% and the 30-year to its highest level in about 19 years — reviving inflation fears and squeezing the valuations of growth stocks, which are priced heavily on future earnings that are worth less when discount rates rise.
A third, more mechanical factor added noise: yesterday (September 10) was Korea’s quadruple witching day, when stock futures, stock options, index futures, and index options all expire at once. These expiries force large positional unwinds, and the aftershocks in supply and demand were still rippling through today’s session.
Who sold $3 billion — and who bought the dip
The selling came from the two big-money camps at once. On the KOSPI, foreign investors net sold 2.4587 trillion won (roughly $1.8 billion at today’s rate) and domestic institutions net sold 1.6443 trillion won (about $1.2 billion) — a combined outflow of over 4 trillion won, or roughly $3 billion, in a single session. Retail investors took the other side, net buying 2.4259 trillion won and cushioning the fall.
The KOSDAQ saw the same pattern at smaller scale: foreigners sold 358.5 billion won and institutions 226.7 billion won, against 571 billion won of retail buying.
One accounting caveat: these figures come from Financial News’ closing tally. Another outlet, Opinion News, reported slightly different final numbers — foreigners at -2.2915 trillion won, institutions at -1.2237 trillion won, retail at +1.8660 trillion won, plus 1.6526 trillion won of buying by “other corporations,” presumed to be company share buybacks. The gap reflects different snapshot times, but the direction of the story is identical: heavy foreign and institutional selling, absorbed by retail and corporate buyers.
Chips bore the brunt; ships and banks were the only green
Higher long-term yields hit the market’s semiconductor heart hardest. Samsung Electronics fell between 3.53% and 4.09% depending on the tally, closing at 259,500 won (about $193). SK Hynix dropped 2.16% to 3.72% to around 1,812,000-1,813,000 won. The pain extended down the supply chain: chip-equipment maker Wonik IPS sank 7.15%, Jusung Engineering 5.43%, Leeno Industrial 4.18%, and Hanmi Semiconductor and Nextin both fell in the 7% range. Battery-materials name EcoPro BM slid 7.08%, and robotics stocks including Rainbow Robotics and Doosan Robotics declined together.
By sector, electricals and electronics fell 2.66% to 3.80%, manufacturing 2.21%, and medical and precision instruments 2.18%; only construction and food-and-beverage sector indices managed to stay positive.
The winners’ list was strikingly short. HD Hyundai Heavy Industries jumped 5.62% to 6.28% on hopes for overseas warship orders, including from the Philippines, plus ongoing defense-export and offshore-plant momentum. Low price-to-book dividend financials also caught a bid — KB Financial Group rose 2.08% to 2.6% (the only gainer among the ten largest KOSPI stocks) and Shinhan Financial Group added 2.09%. Banks tend to earn more when rates rise, so they are a natural hiding place on a day like this.
Today’s key numbers
| Metric | Level | Change |
|---|---|---|
| KOSPI (official close) | 6,909.91 | -1.76% (-124.01 pts) |
| KOSDAQ (official close) | 820.64 | -1.95% (-16.28 pts) |
| USD/KRW (quoted level, continuous trading) | around 1,344 | about +0.4% |
| WTI crude, Oct (quoted level, continuous trading) | above $100 | Overnight surge |
| Brent crude, Nov (quoted level, per E-Today) | $105.38 | +4.1% |
| US 10-year Treasury yield (quoted level, overnight session) | around 4.95% | — |
| Foreign net flow, KOSPI | -2.4587T won (~$1.8B) | Net sell |
What to watch next
- US August CPI, tonight at 9:30 PM Seoul time (8:30 AM US Eastern). It is the key variable ahead of the September 17 FOMC rate decision — especially after Fed Governor Waller and New York Fed President Williams both suggested no further hikes are needed if inflation holds at current levels.
- The Middle East and oil. A prolonged or widening US-Iran conflict could push crude higher still and put global inflation back on the table.
- The 7,000-7,500 overhang. SK Securities and others see the KOSPI capped near 7,500 in the short term, citing fading semiconductor re-rating momentum and worsening flows, and argue a quick reclaim of the prior highs above 7,000 will be difficult, per Edaily. Analysts estimate roughly 20 trillion won (~$15 billion) of retail positions bought in the 7,000-7,500 zone are waiting to sell into any rebound.
FAQ
Why did the KOSPI fall on September 11, 2026?
Two overnight shocks: WTI crude broke above $100 a barrel on escalating US-Iran conflict near the Strait of Hormuz, and US Treasury yields spiked, with the 10-year reaching around 4.95% overnight. Both hit the valuations of Korea’s dominant semiconductor stocks, and foreign investors and institutions together sold over 4 trillion won (~$3 billion) of KOSPI shares.
Who was buying Korean stocks during the selloff?
Retail investors. Individuals net bought about 2.43 trillion won (~$1.8 billion) on the KOSPI and another 571 billion won on the KOSDAQ, absorbing much of the foreign and institutional selling and helping the index close well above its intraday low.
What is quadruple witching, and why does it matter here?
It is the simultaneous expiration of stock futures, stock options, index futures, and index options — in Korea it fell on September 10, the day before this selloff. Expiries force large mechanical position unwinds, and the resulting flow distortions can add volatility for a session or two afterward.
Did any Korean stocks rise today?
Very few. HD Hyundai Heavy Industries gained over 5% on warship-order hopes, and KB Financial Group — the only riser among the ten largest KOSPI stocks — rose about 2%, alongside Shinhan Financial Group. Construction and food-and-beverage were among the only sector indices to close positive.
Disclaimer: This is an information and analysis publication, not investment advice. See our Methodology for data sources, standards, and our corrections policy.
Related reading
Also on Seoul Closing Bell
A companion piece on the same session, written from a different angle: KOSPI Absorbed 4 Trillion Won of Selling — Retail Held the Line.