KOSPI Plunges 5.8% as Sell Sidecar Triggered Amid Global Chip Selloff and Surging Bond Yields Worldwide

SEOUL — South Korea’s benchmark KOSPI index plunged 398.66 points, or 5.80%, to close at 6,471.17 on Wednesday, its second consecutive day of sharp declines, as a global selloff in semiconductor stocks combined with surging bond yields and renewed Middle East tensions to rattle investors across Asian markets.

The Korea Exchange activated a sell-side sidecar, a mechanism that temporarily suspends program sell orders, at 9:06 a.m. local time after the index tumbled as much as 5.6% within the first minutes of trading. The KOSPI opened at 6,528.77, down 4.96% from the previous session, before losses widened further as the morning progressed, briefly touching 6,430.93 points, a decline of 6.39%, before settling into a range around the 6,400 to 6,500 level for the remainder of the session.

South Korea’s chipmakers bore the brunt of the selling. According to Trading Economics, Samsung Electronics and SK Hynix plunged 7.54% and 9.93%, respectively, tracking steep losses in U.S. semiconductor stocks overnight. Other major names also fell sharply: SK Square dropped 11.54%, Hyundai Motor fell 5.17%, Kia Corporation slid 3.21%, KB Financial Group declined 1.72% and HD Hyundai Heavy Industries dropped 3.06%. By sector, only construction, up 1.84%, and pharmaceuticals, essentially flat with a 0.01% gain, avoided the broad selloff, while utilities and electronics sank 7.68%, manufacturing fell 6.36%, insurance dropped 5.89%, finance declined 4.81%, securities fell 4.6% and distribution dropped 4.45%, according to figures reported by the Asia Business Daily.

Trading volume data underscored a split between retail and institutional sentiment. Foreign investors were net sellers of roughly 3.4883 trillion won, while institutional investors sold a net 1.3244 trillion won. Individual investors, by contrast, were significant net buyers, purchasing a net 4.6368 trillion won worth of shares, suggesting many retail traders viewed the sharp decline as a potential buying opportunity even as larger institutional and foreign players continued pulling back.

The selloff extended across the region. Japan’s Nikkei 225 fell 3.16% to close at 65,326.42 points, marking its own second consecutive day of losses and hitting its lowest closing level in nearly two weeks, according to TradingKey. The regional downturn was driven primarily by a broader global technology selloff, with surging U.S. Treasury yields, which reached multi-year highs, prompting investors to reassess high valuations across the technology sector. Adding to the pressure, escalating tensions in the Middle East pushed crude oil prices higher, stoking inflation concerns and raising fears that central banks might have less room to cut interest rates than markets had previously anticipated.

U.S. President Donald Trump added to the uncertainty Tuesday by stating that the United States was not currently in talks with Iran, a comment that further undercut hopes for a resolution to stalled diplomatic efforts and raised fears of continued disruption to Middle East oil supplies, according to Trading Economics.

Wednesday’s plunge came after an already volatile session Tuesday, during which the KOSPI had briefly surged more than 3% in early trading to reclaim the 7,200 level, before institutional selling dragged the index back down to close at 6,869.83 points, a decline of 1.55% for the day despite the earlier intraday gains. That roller-coaster pattern has become increasingly common for the index throughout 2026, reflecting a market that has repeatedly swung between sharp rallies and equally sharp reversals over the course of the year.

The chip sector’s troubles were not confined to South Korea. According to TradingKey, U.S. memory chipmaker Micron Technology saw its shares plunge more than 7% overnight, with some technical analysts warning of potential further downside risk of as much as 20%, while Japanese flash memory maker Kioxia fell over 10% and Western Digital also posted steep losses, reflecting a broad-based retreat across the global memory chip industry that had otherwise been one of the strongest-performing corners of the market for much of the year.

Despite Wednesday’s sharp losses, the KOSPI remains up substantially over the past year. According to Trading Economics, the index remains 106.74% higher than it was a year ago, even after declining 0.69% over the trailing month, underscoring both the scale of the index’s extraordinary rally throughout 2026 and the severity of the volatility that has periodically interrupted that broader upward trajectory.

Wednesday’s decline adds to a growing tally of significant single-session swings the KOSPI has experienced this year. According to earlier reporting from the Seoul Economic Daily, the index has triggered 18 sell sidecars and seven circuit breakers so far in 2026, a pace of volatility that market analysts have repeatedly linked to concerns over the sustainability of capital spending tied to the broader artificial intelligence boom, alongside heavy concentration risk given that Samsung Electronics and SK Hynix together account for roughly half of the KOSPI’s total market capitalization.

Adding a note of longer-term significance amid the day’s turmoil, reports emerged that SK Hynix had reached a key turning point in its 2026 wage negotiations, which had previously been deadlocked over the formula used to allocate a record employee bonus, according to TradingKey. Separately, the Financial Times reported that Nvidia’s H200 artificial intelligence chips had been approved to enter the mainland Chinese market in small batches, a development that could carry longer-term implications for the broader AI chip supply chain even as markets focused primarily on the day’s steep losses.

With global bond yields continuing to climb and Middle East tensions showing no clear sign of resolution, investors are likely to remain focused in the coming days on whether Wednesday’s sharp selloff represents a short-term correction within an otherwise strong yearlong rally, or the beginning of a more sustained reassessment of the elevated valuations that have characterized semiconductor and technology stocks across both South Korea and global markets throughout much of 2026.