South Korea's KOSPI fell more than 3% on spillover from sharp declines in U.S. artificial intelligence and tech stocks, including Alphabet. The index slid to the 5,600 level during the session, triggering a sell-sidecar for the first time in 11 sessions. Foreigners net sold more than 1.6 trillion won in the main board market.

On Oct. 30, the KOSPI ended down 206.92 points, or 3.48%, at 5,730.74. It opened down 177.31 points, or 2.99%, at 5,760.35 and slid as far as 5,599.42, widening its decline to more than 5%. Bargain hunting later emerged, and the index recovered about 130 points from the intraday low to hold the 5,700 level.

The intraday slump also triggered a sell-sidecar. The Korea Exchange halted the effectiveness of program sell orders in the main board market for 5 minutes after KOSPI 200 futures fell 5.12% from the reference price of 935.84 to 887.92 at 10:04:55 a.m.

It was the first time a sell-sidecar was triggered in the main board market in 11 sessions since Oct. 15, when the KOSPI plunged.

By investor type, foreigners were net sellers of 1.617 trillion won, weighing on the index. Retail investors and institutions were net buyers of 620.5 billion won and 742.7 billion won, respectively.

Among the top market-cap stocks, semiconductor-related shares posted the steepest declines.

SK Hynix ended down 7.08% at 1,418,000 won, while Samsung Electronics fell 3.02% to 225,000 won.

SK Square fell 5.88% and Samsung Electro-Mechanics slid 7.50% in sharp declines. Hyundai Motor fell 3.59%, KB Financial Group lost 0.83%, and Samsung Life Insurance dropped 2.70%.

Samsung Biologics surged 8.86%, while LG Energy Solution rose 0.98%.

The KOSDAQ also extended losses. It ended down 28.85 points, or 3.83%, at 724.38.

In the Seoul foreign exchange market, the won-dollar exchange rate was 1,334.00, down 6.50 won from the previous session.

The sharp fall in local stocks was influenced by weakness in U.S. tech shares the previous day. Alphabet, Google's parent, plunged 12.6% as results missed market expectations and concerns grew over rising AI investment costs. The Nasdaq index fell 1.37%, and the Philadelphia Semiconductor Index dropped 1.4%.

Volatility increased as foreign selling focused on semiconductor stocks such as Samsung Electronics and SK Hynix, which recently led the rebound in local stocks. Still, the KOSPI pared some losses from its intraday low, showing signs that bargain hunting also emerged after the plunge.

Han Ji-young (한지영), a researcher at Kiwoom Securities, said local stocks opened lower under the influence of Alphabet's sharp drop in the U.S. session and weakness in semiconductor shares. She said it is reasonable at the current point, after repeatedly facing sharp declines while already pricing in related concerns, to keep low the possibility of entering a phase of testing the previous low.