South Korea's benchmark KOSPI opened 4.96% lower and fell as much as 6.4% in early trading, triggering a market stabilization mechanism as a global semiconductor selloff spilled into Asian equities.

The Korea Exchange activated the sell-side sidecar at 9:06 a.m. local time, temporarily suspending program sell orders for five minutes after KOSPI 200 futures remained at least 5% below their previous close for one minute. The sidecar sits below the exchange's market-wide circuit breakers in severity: rather than halting all trading, it suspends only program orders in futures, a design meant to slow algorithmic selling while other trading continues. The index later recovered part of the decline and was trading around 5.2% lower at 6,515.97 during the session.

Samsung and SK Hynix lead the rout

Samsung Electronics fell as much as 7.7% during the early selloff, while SK Hynix dropped more than 9% as investors cut exposure to the two stocks that have dominated South Korea's AI-driven equity rally. The two companies are the heaviest-weighted stocks on the KOSPI, giving their moves outsized influence on the benchmark. Samsung is the world's largest memory-chip maker and SK Hynix is the leading supplier of the high-bandwidth memory (HBM) used in AI accelerators, linking their valuations to the same AI-demand cycle that drives U.S. peers such as Nvidia and Micron. Losses moderated later in the session, with Samsung down about 6.9% and SK Hynix off 7.9%.

The declines followed another weak Wall Street session in which the Philadelphia Semiconductor Index dropped 5.6%, Micron lost roughly 7% and Nvidia fell more than 2%.

Korean chip stocks have already experienced repeated bouts of extreme volatility this year. The KOSPI plunged nearly 10% in June as Samsung and SK Hynix each lost more than 12%, and an earlier June rout triggered a 20-minute market-wide trading halt after the index dropped more than 8%.

Sidecar count reaches 48 in 2026

Wednesday's intervention was the 48th KOSPI sidecar activation of 2026, including 25 sell-side and 23 buy-side triggers. That count is substantially higher than the 10 events cited in some early market summaries.

Volatility in South Korea has intensified alongside the rapid growth of leveraged products tied to Samsung, SK Hynix and other AI-linked shares. Semiconductors are also South Korea's largest export category, so the sector's fortunes matter well beyond the equity market. Similar swings spilled into crypto-linked markets earlier this month, when Trade.xyz compensated SK Hynix traders following a 19% mark-price dislocation.

Nikkei drops as Asian tech weakness spreads

The selloff extended beyond Seoul. Japan's Nikkei 225 fell about 2.6% to 65,703.78, Taiwan's Taiex dropped 1.4%, and Hong Kong's Hang Seng declined about 0.4%.

Rising global bond yields and higher oil prices added pressure to technology valuations, alongside renewed concerns over AI-sector pricing. U.S. semiconductor weakness provided the immediate catalyst after South Korean stocks had rallied for six consecutive sessions through Tuesday.

Later on Wednesday morning, the KOSPI remained about 5.2% lower at 6,515.97 after recovering from its early decline of more than 6%.