The main index in Seoul shed 322.7 points to 6,272.8, a drop of 4.9 percent.
Samsung Electronics fell 7.8 percent and SK hynix 7.5 percent, pulling the large-cap KOSPI 200 down 5.3 percent while the KOSDAQ lost only 0.35 percent to 718.18.
Tokyo slipped as well, even though Wall Street had closed higher on Friday, marking the retreat as a local unwind of an unsustainable one-day spike rather than an imported selloff.
Foreign investors sold a net 795.6 billion won, or about $555.1 million, on the main board, against 801.9 billion won of buying by individuals.
That is a mirror image of Friday, when foreigners bought a net 7.22 trillion won on the KOSPI, the largest single-session total on record, and retail investors sold into the rally.
The main index closed July 31 at 6,595.45, up 17.91 percent, the steepest one-day gain in its history.
Samsung Electronics traded at 242,000 won, or about $168.80, and SK hynix at 1,590,000 won, or about $1,109.20. SK hynix had closed at its daily upper price limit on Friday, its first limit-up in roughly 17 years.
Even inside the large-cap chip complex the moves diverged. SK square, which holds the controlling stake in SK hynix, fell 3.6 percent to 1,001,000 won, or about $698.30, while Samsung Electro-Mechanics rose 2.2 percent to 1,167,000 won, or about $814.10.
Buying rotated toward sectors with no memory exposure. Airlines led the sector board with a gain of 4.3 percent and wireless telecom services added 3.9 percent.
In Tokyo, the Nikkei 225 was down 1,016.2 points, or 1.6 percent, at 63,345.9, also surrendering part of Friday's advance.
The won was quoted at 1,433.50 to the dollar in Hana Bank's morning posting, down 6.50 won.
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