The benchmark Kospi Index slid as much as 9.8%, triggering a circuit breaker for a second straight day. The gauge is on course for a record monthly loss of about 35%, after a world-beating rally earlier this year that relied almost entirely on two chipmakers: SK Hynix and Samsung Electronics Co.

The unprecedented back‑to‑back suspension for Kospi trading underscores investors' doubts over the AI boom. The benchmark has now lost about 40% from its peak a month ago, with the selloff accelerating as investors question the business case for the massive investment pouring into the industry.

SK Hynix tumbled as much as 15% Wednesday after its earnings call with analysts ended with scant details on shareholder returns and its long-term contracts with clients. The company, whose two-day drop amounted to about a quarter of its value, said it would boost its capital spending to at least $31 billion after reporting a six-fold surge in quarterly profit.

"SK Hynix is lifting capex to the high 40 trillion won range, while staying silent on shareholder returns and the pricing inside its long-term contracts, and that's left investors feeling uneasy," said Josh Gilbert, lead analyst for Asia Pacific and the Middle East at Etoro Ltd. "Given the weight of SK Hynix and Samsung on the Kospi, there's nowhere to hide when they fall together."

The Kospi slid below the 6,000 mark on Wednesday to the lowest level since early April. Investors are now awaiting earnings results from Samsung Electronics on Thursday and other US big technology companies this week.

The Kosdaq Index of smaller and medium sized companies also slid more than 8%, triggering a circuit breaker earlier, that involves a trading halt for 20 minutes. Of the 15 circuit breakers in the benchmark Kospi since 2000, no fewer than nine have taken place this year.

'Forced Liquidations'

Retail investors, who have helped fuel the rally in Korean shares this year through stock margin loans and leveraged exchange-traded funds, were net sellers on Wednesday. They cut their holdings by about 1.7 trillion won ($1.2 billion).