Seoul's benchmark KOSPI fell 123.49 points or 1.8 percent to close at 6,788.88.
The losses were concentrated among large-cap stocks. The KOSPI 200 fell 2.1 percent, while the tech-heavy KOSDAQ edged up 0.1 percent to close at 838.41.
SK hynix took the heavier hit. The chipmaker fell 4.5 percent to 1,653,000 won (US$1,204). Samsung Electronics lost 3.4 percent to 257,000 won ($187). The split between the two ran the wrong way for the index, with the more expensive and more heavily owned of the pair falling faster.
Tokyo told the same story in miniature. Kioxia, the Japanese flash-memory maker, dropped 8.8 percent. Advantest, which makes chip-testing equipment, gained 1.9 percent.
Traders read that gap as selling aimed at memory pricing rather than at artificial intelligence spending broadly, a distinction that spares equipment makers and hits Korea directly.
Foreign investors sold a net 1.76 trillion won ($1.28 billion) on the main board, with institutions selling a further 284.4 billion won ($207.2 million). Individuals bought 424.5 billion won ($309.3 million).
Samsung Biologics fell 6.8 percent to 1,486,000 won ($1,083).
Outside the index leaders the market held up. KB Financial Group added 2.1 percent to 171,600 won ($125). Gains also ran through autos, power equipment and electronic components.
In Tokyo, the Nikkei 225 closed at 66,405.56, up 0.4 percent. The composite index in Shanghai was modestly higher.
The won firmed to 1,372.50 per dollar, stronger by 9.50 from the previous sesson.
The breadth is the bulls' argument and it is a thin one. A market where financials, autos and components all rise and the index still loses nearly 2 percent has not diversified away from memory. It has simply narrowed the bet.
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