Korea Market Brief — KOSPI rebounds 5.89% as SK hynix unveils a 40 trillion won buyback (Aug 20)

Seoul's benchmark index spent Thursday undoing almost exactly what it had done the day before. A session after the KOSPI dropped 5.55% in the worst of this week's global bond-market turmoil, it closed at 6,852.58, up 5.89% — and the trigger was not a change of heart about long-term interest rates. It was a number released after Wednesday's bell: 40 trillion won.

The short version: SK hynix announced a 40 trillion won buyback-and-cancellation program, and Samsung Electronics is reported to be preparing a shareholder return package of its own worth more than 100 trillion won. Foreign investors bought a net 1.7 trillion won of Korean stock, the won firmed to 1,392.6 per dollar, and Seoul clawed back most of Wednesday's losses.

What moved the market

The index opened 3.23% higher and kept going. By 9:57 a.m. a buying-side sidecar had been triggered — the 49th sidecar activation on the KOSPI this year, a statistic that says as much about 2026's volatility as any single day's move does.

The catalyst was SK hynix. After Wednesday's close the company announced a 40 trillion won share buyback and cancellation program — roughly $29 billion at Thursday's exchange rate — and, more importantly for how the stock gets valued from here, committed to returning at least 50% of cumulative free cash flow to shareholders. The stock had been under profit-taking pressure after a long run; the announcement reversed that in a single session, sending it up 12.73% to 1,691,000 won.

The read-across was immediate. Samsung Electronics rose 9.49% to 271,000 won on reports that it is preparing a shareholder return program worth more than 100 trillion won, with details not yet finalized. Between the two companies, that is a scale of announced and rumoured capital return that Korean large caps have historically not done, and it lands in the middle of an AI memory cycle that is generating the cash to fund it.

Flows told a familiar Seoul story. Foreign investors bought a net 1.7 trillion won (about $1.2 billion). Institutions sold a net 219.5 billion won and retail investors sold a net 2.3 trillion won — domestic money using the bounce to lighten up, offshore money doing the buying. That split has been the shape of this rally for most of August.

The second ingredient came from overnight. On Wednesday in New York, the US Treasury said it would at least double the maximum size of its liquidity-support buyback operations in longer-dated coupon securities, lifting the cap from $2 billion to a minimum of $4 billion for the 10-to-20-year and 20-to-30-year sectors, effective September 9 through early November. The 10-year yield fell about five basis points to 4.65% and the 30-year gave up nine to 5.19%, after the long bond had touched its highest level since 2007 earlier in the week. US stocks snapped a three-day losing streak, with the Dow, S&P 500 and Nasdaq each adding roughly 0.2%.

That was enough to take the pressure off. This week's Seoul selloff was never really about Korean fundamentals — it was long-end yields repricing globally and hitting the most crowded, longest-duration trade on the board, which in Korea means the chipmakers. When the yield story softened, the same names came back hardest.

Sector by sector

Semiconductors were the whole story on the KOSPI. The two chip heavyweights account for such a large share of the index that a 12.73% move in SK hynix and a 9.49% move in Samsung Electronics mechanically explain most of the 5.89% index gain. Anyone modelling Korea as a broad risk-on trade on Thursday would be over-reading it.

Pharmaceuticals and biotech led the KOSDAQ, which rose 1.99% to 840.89. The driver was imported: Moderna reported positive late-stage results for a melanoma vaccine developed with Merck, and its shares soared in New York, pulling Korean biotech names up in sympathy. Sympathy rallies of this kind tend to fade unless domestic pipeline news follows, so treat the KOSDAQ's move as thinner than the headline.

The rest of the market — autos, shipbuilding, defense, financials — participated but did not lead. The gap between the KOSPI's 5.89% and the KOSDAQ's 1.99% is the clearest single measure of how concentrated the day was.

The won and the macro picture

The won closed at 1,392.6 per dollar, stronger by 5.1 won. That extends a notable move: the rate slipped below 1,400 on Wednesday for the first time in roughly eleven months. A firmer won alongside a rising KOSPI is the classic signature of foreign inflows into Korean equities, and it lines up with the 1.7 trillion won of net buying.

The policy backdrop is unusual for Korea. The Bank of Korea raised its base rate 25 basis points to 2.75% on July 16, its first increase in about three and a half years, with AI-driven semiconductor exports pushing growth and inflation higher. Minutes from that meeting, released in early August, showed four of six Monetary Policy Board members flagging the need for a further hike, with two preferring to wait for more data. The next BOK meeting is August 27.

That is the tension worth holding onto. Korea's export cycle is running hot enough to make its central bank tighten while much of the world is still debating cuts — semiconductor exports rose sharply year-on-year through the middle of the year, and monthly exports have been setting records. A stronger won takes some edge off imported inflation, which marginally reduces the pressure on the BOK; a chip boom that keeps feeding through to wages and prices does the opposite.

What to watch next

• August 21 (Friday), Korea Customs Service 20-day export data. The first-20-days figures for August are the fastest read on whether the semiconductor export surge is still accelerating. Chip export growth, and the average daily export figure rather than the raw total, are the numbers that matter.
• August 27, Bank of Korea rate decision. A divided board and an above-target inflation print make this a live meeting rather than a formality. Watch the vote split as much as the decision.
• Samsung Electronics' shareholder return announcement. Reported but not confirmed. If the package lands near the figures being discussed, it reprices the stock; if it disappoints or slips, Thursday's 9.49% gain has little underneath it.
• The US long end. The Treasury's buyback expansion does not take effect until September 9. Between now and then, 30-year yields are the variable most likely to decide whether Seoul holds this bounce.

Thursday was a rebound with a specific cause, not a broad re-rating. Two companies made capital-return announcements into a market that had just been forced to sell them, and offshore buyers took the other side. Whether that holds depends less on Seoul than on where global long-term yields settle over the next few weeks — which is roughly what this whole week has been about.

This is market information, not investment advice.