Seoul — August 31, 2026. Published after the market close; prices are official closing values.
The 30-second version
- The KOSPI closed at 6,820.02, up 0.46% — after opening down 2.58% and touching 6,547.76 intraday, a drop of more than 3% from the prior close.
- The turnaround driver: ongoing share buybacks by Samsung Electronics (15 trillion won, roughly $10.9 billion) and SK hynix (40 trillion won, roughly $29 billion) absorbed heavy foreign and passive-fund selling tied to the MSCI Korea Index rebalancing.
- The KOSDAQ could not complete the same comeback, closing down 0.49% at 834.29 as Ecopro-group battery stocks fell 2-4%.
- Retail investors bought the dip (roughly +330 billion won, about $240 million); foreigners and institutions were net sellers, concentrated in semiconductors.
- The won strengthened, with USD/KRW closing at 1,370.01, down 10.49 won (-0.76%).
A brutal open, imported from the US
Monday’s session began with the kind of drop that usually defines the day. The KOSPI opened at 6,613.58, down 2.58%, and kept sliding to an intraday low of 6,547.76. Two overnight catalysts did the damage. First, Fed Chair Kevin Warsh struck a hawkish tone in his Jackson Hole keynote, saying summer inflation data had been better than expected but that the core inflation trend had not meaningfully improved — reviving upward pressure on long-term rates. Second, US chip stocks had been hammered in Friday’s session (August 28): the Philadelphia Semiconductor Index fell 3.47%, Nvidia dropped 4.57%, Intel 2.85%, and AMD 2.33%. Note that those are the prior US session’s moves, not Monday’s — but they set the tone, and Korea’s semiconductor heavyweights opened down around 3% in sympathy. A separate worry added fuel: Google’s newly unveiled AI compression algorithm, TurboQuant, stoked concerns about softer memory-chip demand.
By the close, all of that was erased on the KOSPI. Local media dubbed it a classic “weak open, strong close.”
The closing-price war: buybacks vs. MSCI passive flows
Monday was the effective date for the MSCI Korea Index August rebalancing, which took effect at the closing price. A quick explainer: when MSCI adds or removes stocks from its indexes, funds that passively track those indexes must buy and sell to match — and they typically do it in the closing auction, a single-price batch trade at the end of the session, to minimize tracking error. That concentrates enormous order flow into the final minutes and can whip prices around.
Against that passive selling stood two very large, very steady buyers: Samsung Electronics and SK hynix themselves. Both are running buyback programs — Samsung’s 15 trillion won program runs through November 21, SK hynix’s 40 trillion won program through November 19. As of August 28, the two had executed a combined roughly 10.28 trillion won (about $7.5 billion): 2.55 trillion won by Samsung and 7.73 trillion won by SK hynix. That leaves roughly 44.7 trillion won — about $32.6 billion — of remaining buying capacity. Think of it as a standing bid under the market’s two largest stocks. On Monday that bid soaked up the foreign and passive selling, and the “closing-price war” between MSCI rebalancing flows and the buybacks resolved in the bulls’ favor: SK hynix finished up 1.27% and Samsung Electronics up 1.17%.
The rebalancing itself, effective September 1, adds LG Innotek to the MSCI Korea Index and removes four names: HLB, LG Display, POSCO International, and Samsung Epis Holdings — the deletions now exposed to passive-fund outflows.
Who bought, who sold — and why the KOSDAQ lagged
Per media tallies near the close (official exchange figures may differ slightly), retail investors were net buyers of roughly 330 billion won (about $240 million) on the KOSPI, treating the plunge as a dip-buying opportunity. Foreigners sold roughly 250 billion won (about $180 million), concentrated in semiconductors and electronics, and institutions sold roughly 140-150 billion won, led by brokerages and private funds. Program trading — automated basket trades — netted out to roughly 290 billion won of selling, with a small 11.9 billion won of arbitrage buying swamped by 303.5 billion won of non-arbitrage selling.
Breadth at the top was strong: 8 of the 10 largest KOSPI stocks closed higher, led by Samsung Electro-Mechanics (+2.60%), LG Energy Solution (+2.16%), and Samsung Biologics (+2.15%). Samsung Life (-1.29%) was the notable large-cap decliner.
The KOSDAQ told a different story. It fell as much as 2.00% early (to 821.67) and clawed most of that back, but without a buyback backstop of its own it stayed in the red. The drag was the battery complex: Ecopro BM fell 2.88%, Ecopro was down in the 2% range, and Ecopro HN in the 4% range.
Key closing numbers
| Measure | Close | Change |
|---|---|---|
| KOSPI | 6,820.02 | +31.14 (+0.46%) |
| KOSPI intraday low | 6,547.76 | — |
| KOSDAQ | 834.29 | -4.12 (-0.49%) |
| USD/KRW | 1,370.01 | -10.49 won (-0.76%) |
| SK hynix | — | +1.27% |
| Samsung Electronics | — | +1.17% |
| Ecopro BM | — | -2.88% |
What to watch next
- September 1, the first session after the MSCI change: most passive rebalancing flow was executed in Monday’s close, but any residual selling in the deleted names (HLB, LG Display, POSCO International, Samsung Epis Holdings) early Tuesday is the thing to watch.
- Buyback firepower: roughly 44.7 trillion won (~$32.6 billion) of combined Samsung/SK hynix buyback capacity remains through mid-to-late November. Whether it keeps acting as a breakwater against foreign selling is the market’s central question.
- Follow-through: after a 3%-plus intraday drop was fully reversed, traders will watch whether the rebound extends into the new month.
- Rates and memory demand: further hawkish Fed signals after Warsh’s Jackson Hole speech, and any follow-on to the TurboQuant memory-demand worry.
FAQ
Why did the KOSPI fall 3% and then recover on August 31, 2026?
It opened sharply lower on Fed Chair Kevin Warsh’s hawkish Jackson Hole remarks and Friday’s US chip rout (SOX -3.47%, Nvidia -4.57%). It recovered because Samsung Electronics and SK hynix buybacks, plus retail dip-buying of roughly 330 billion won, absorbed foreign and MSCI-related passive selling. The index closed up 0.46% at 6,820.02.
What changed in the MSCI Korea Index rebalancing?
Effective September 1, LG Innotek joins the index while HLB, LG Display, POSCO International, and Samsung Epis Holdings are removed. Index-tracking funds executed most of the resulting buys and sells at Monday’s closing auction, which amplified end-of-day volatility.
How big are the Samsung Electronics and SK hynix buybacks?
Samsung’s program is 15 trillion won (through Nov 21) and SK hynix’s is 40 trillion won (through Nov 19). As of August 28 they had executed a combined ~10.28 trillion won, leaving roughly 44.7 trillion won — about $32.6 billion — still to deploy.
Why did the KOSDAQ close lower while the KOSPI rose?
The KOSDAQ lacked the buyback support propping up the KOSPI’s chip giants, and its heavyweight battery names sold off — Ecopro BM fell 2.88%, with Ecopro and Ecopro HN down 2-4% — capping its rebound at a 0.49% loss.
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: Samsung and SK Hynix Buybacks Beat MSCI Rebalancing Flows.