South Korea's KOSPI index fell 10 percent on Tuesday, triggering a 20-minute trading halt under circuit-breaker rules designed to slow panic selling. SK Hynix and Samsung Electronics each declined more than 12 percent as investors reassessed whether artificial intelligence infrastructure spending justifies valuations across the semiconductor supply chain.

The shock spread through Asian and U.S. sessions: Japan's Nikkei dropped 3.6 percent, SoftBank fell 15 percent, and U.S. technology indexes extended losses for a second day. Korean regulators said they monitored foreign outflows but found no evidence of coordinated short attacks.

Why Korea Led the Decline

SK Hynix and Samsung derive outsized revenue from high-bandwidth memory sold to Nvidia and hyperscalers. When investors question AI demand, Korean equities absorb disproportionate impact because memory makers lack diversified consumer businesses large enough to offset data-center cyclicality.

The KOSPI had rallied more than 90 percent before Tuesday's drop, leaving valuations stretched even by bullish standards. Analysts described the move as violent price discovery inside a structural bull case rather than a fundamental collapse of AI demand.

Global Contagion

U.S. names including Micron, AMD, and Intel sold off in sympathy. Leveraged ETFs tracking semiconductor baskets amplified declines. The Nasdaq remained up roughly 10 percent year-to-date despite the correction — context bulls cited to argue the selloff was overdue profit-taking.

Bears pointed to hyperscaler capex exceeding $452 billion in 2026 and questioned whether revenue growth will arrive fast enough to justify current multiples. Federal Reserve rate policy played a secondary role; strategists framed the episode as sector-specific.

Policy Response

Korea's financial supervisory service convened emergency monitoring sessions but did not announce intervention beyond existing circuit-breaker mechanics. Pension funds' semiconductor overweight positions face scrutiny in parliamentary hearings scheduled for July.

Memory makers issued no revised guidance during the selloff. Micron's subsequent record earnings later in the week partially reversed sentiment, illustrating how single-supplier prints can swing the narrative.

Outlook

Traders will watch Korean export data and U.S. cloud earnings for confirmation whether Tuesday marked a shakeout or the start of a deeper derating. For Seoul, the episode reinforced dependence on a single technology cycle — profitable when AI builds accelerate, punishing when sentiment turns.