South Korea halts stock trading for a second straight day. what this could mean for investors, AI and global markets.

Trading on South Korea’s stock market was temporarily halted on Wednesday, July 29, after a sharp sell off in semiconductor shares triggered the exchange’s emergency safeguards. The Korea Exchange first suspended trading on the KOSDAQ, a market dominated by technology and smaller growth companies, before halting the KOSPI, the country’s main index of large listed companies. Trading on both markets was paused for 20 minutes.

The sell off triggered circuit breakers, an emergency mechanism that temporarily halts trading when markets fall sharply to give investors time to absorb new information and reduce panic selling. Trading on both markets was paused for 20 minutes after the KOSDAQ fell 8.05% to 649 and the KOSPI dropped 8.15% to 5,532.33. It was the first time circuit breakers had been activated across both South Korean markets on two consecutive trading days.

Before the full trading halt, the exchange had activated sell side sidecars, which temporarily suspended automated programme sell orders for five minutes as the decline intensified. Unlike circuit breakers, sidecars do not stop the entire market. They are intended to slow a sudden wave of computer generated selling before it develops into a broader market collapse. The intervention failed to calm the sell off and the KOSPI fell almost 10% after trading resumed before recovering part of its losses later in the session.

The renewed selling on Wednesday followed an even steeper decline in the previous session, when the KOSPI closed 10.84% lower at 6,023.66. Samsung Electronics fell 14.4%, while SK Hynix lost 14.7%. Because the two chipmakers together account for more than half of the KOSPI’s weighting (their combined influence on the index), sharp declines in their shares can pull the broader market significantly lower, even when losses among other listed companies are less severe.

The pressure on chip shares reflects several concerns. Investors are increasingly questioning whether the enormous sums being spent on artificial intelligence data centres and advanced semiconductors will generate strong enough financial returns. SK Hynix also came under pressure after reporting record quarterly operating profit (earnings from its main business before interest and taxes) that still fell short of analysts expectations.

Another factor weighing on semiconductor stocks is growing competition from China. The successful stock market debut of Chinese memory chip producer CXMT raised expectations that it could use the funds raised to expand production and compete more aggressively with established manufacturers such as Samsung Electronics and SK Hynix. Semiconductor investors were also unsettled by reports that China had begun producing domestically developed immersion DUV lithography equipment (machines used in the production of chips), signalling further progress in its efforts to build a more independent chip industry.

The turmoil shows how closely South Korea’s stock market has become tied to the global AI boom. Samsung Electronics and SK Hynix remain major suppliers of the memory chips used in AI systems, but their rapid declines demonstrate how quickly confidence can reverse when even record profits fail to meet extraordinary expectations. The question now is not simply whether AI demand will continue growing, but whether that growth can justify the valuations and enormous spending built around it.