The benchmark rose 3.5 percent, recovering roughly a third of the 910.71 points it lost in Tuesday's record plunge.
Samsung Electronics led, jumping 7.4 percent to 333,000 won ($217), while SK hynix rose 4.4 percent to 2,667,000 won ($1,738); both had shed about 12 percent a day earlier. In Tokyo, the Nikkei 225 firmed 0.4 percent to 70,067.02, steadying after its own 3.5 percent fall.
The snap-back is a familiar one.
The KOSPI's record 12.1 percent crash on March 4 gave way to a 9.6 percent surge the next session, and an 8 percent slide on June 8 was followed by a 4.8 percent rebound on June 9. By one tally in Korean media, eight of the index's 10 worst single-day falls were met by a gain the following day.
Retail investors are again doing the lifting. Individuals bought a net 714.3 billion won in early trade, while foreign investors sold 646.7 billion won and institutions another 103.0 billion won — a near-mirror of Tuesday, when locals absorbed record foreign selling.
The bounce is as narrow as the rally that preceded it.
The junior KOSDAQ added just 0.3 percent to 894.21, and more stocks fell than rose even as the index climbed.
SK hynix, Samsung Electronics, SK Square and Samsung Electro-Mechanics alone made up 63.2 percent of the index at Tuesday's close, by Yuanta Securities' count, so the market now rises and falls largely on four names.
Analysts read Tuesday's plunge as a technical unwind, not a fundamental one. Kiwoom Securities' Han Ji-young noted that oil, the U.S. 10-year yield and the dollar had barely moved, calling it a problem of "speed and concentration."
Mirae Asset Securities' Kim Seok-hwan framed it as event disappointment meeting technical supply pressure, not damage to the earnings outlook. Yuanta's Lee Jae-won called the drop a "rite of passage" after the index cleared 9,000
Tuesday's fall was the KOSPI's largest single-day point drop on record and its fifth-largest by percentage, and triggered the year's fourth circuit breaker. It came a session after SK hynix overtook Samsung Electronics as Korea's most valuable listed company, and tracked an overnight slide in U.S. technology shares.
But the direction of influence soon reversed. Korea's AI-driven rout reverberated across the Pacific, dragging the Nasdaq down 2 percent and the Philadelphia Semiconductor Index (SOX) more than 7 percent lower, underscoring how Seoul has become a global transmission channel for semiconductor risk rather than merely a recipient of it.
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