U.S. semiconductor corporations Micron posted results that beat market expectations, sending the KOSPI surging on the 25th to just shy of the 9,000 mark. SK hynix jumped 14% intraday, briefly overtaking Samsung Electronics to take the No. 1 spot in market capitalization (common shares) for a moment.
The KOSDAQ market, by contrast, froze. The KOSDAQ index opened higher but fell below the 900 level as selling intensified during the session.
The KOSPI index closed at 8,930.30, up 459.28 (5.42%) from the previous trading day. After a 500-point surge early in the session, the index topped the 8,900 level and triggered a buy-sidecar. It was the 28th activation this year alone. The index then steadily climbed to reclaim the 9,000 level before giving back a bit of its gains just before the close.
In the KOSPI market, institutions were net buyers of 3.3 trillion won. Exchange-traded fund (ETF) money accounted for 2.4 trillion won in net purchases, and investment trusts bought a net 760 billion won. National pension funds, which had turned to net buying intraday, were net sellers of 2.5 billion won just before the close. Individuals and foreigners were net sellers by 2.5 trillion won and 820 billion won, respectively. Foreigners extended their net selling to five straight trading days through today, unloading a total of 12.5 trillion won.
SK hynix's rally stood out. News broke the previous day that it issued American depositary receipts (ADR) and would raise 45 trillion won in facility funds in the United States, and Micron's strong results lifted expectations for second-quarter earnings, which is seen as driving the stock's surge. Shares had already jumped in the premarket before the open, and early in the session the static volatility interruption (VI) was triggered, shifting to single-price trading for two minutes.
Before Korea's market opened, Micron said revenue for its fiscal third quarter of 2026 (March–May) was $41.46 billion (about 64 trillion won), up 345.7% from a year earlier. The operating margin was 81.2%. Adjusted earnings per share (EPS) were $25.11, well above the market consensus of $20.78.
Thanks to Micron's "surprise results" announcement, the artificial intelligence (AI) overheating theory that began in Korea's stock market two days earlier and also drove down U.S. stocks has eased significantly.
Samsung Electronics also jumped 5%. Despite SK hynix's strong run, Samsung Electronics still has the larger market capitalization when including both common and preferred shares. Samsung C&T, whose equity value was highlighted by Samsung Electronics' stake, surged 7%, and Samsung Life Insurance rose 3%.
Lee Kyung-min, a researcher at Daishin Securities, said, "Micron's earnings release confirmed medium- to long-term demand and sales visibility through strategic customer agreements (SCA), easing concerns about a slowdown in semiconductor demand," and added, "As a result, investor sentiment for semiconductor stocks recovered and the KOSPI index rose."
The KOSDAQ, meanwhile, fell 2.36% to close at 887.81. It opened higher but gave up the 900 level on institutional selling. Institutions were net sellers of 170 billion won, mostly ETF money. Individuals and foreigners were net buyers of 140 billion won and 20 billion won, respectively.