South Korea, Japan, and Taiwan saw a combined estimated $400 billion erased from equity values on Wednesday as a technology-led sell-off swept across Asian markets, with investors pulling back from semiconductor shares amid concerns over stretched valuations and artificial intelligence spending.

South Korea bore the brunt of the decline. The KOSPI closed 6% lower after plunging as much as 12.6% earlier in the session, triggering a market-wide circuit breaker for the second consecutive day. The losses followed Tuesday's near-11% drop.

KOSPI Extends Historic Decline

The Korea Exchange halted trading for 20 minutes after losses breached the circuit-breaker threshold. The single session removed approximately $180 billion in market value under one widely circulated estimate.

The KOSPI has now fallen nearly 40% from its peak, reached just over a month ago. Trading volume remained low, indicating buyer hesitation during the steep decline. Forced selling intensified as brokers liquidated leveraged retail positions — the same trades that had previously fueled the rapid ascent of South Korean technology stocks.

SK Hynix and Samsung Drive Losses in Seoul

SK Hynix reported a sixfold increase in quarterly profit, but the results fell short of elevated analyst expectations. The company's shares plunged nearly 20% intraday before closing 9.6% lower.

Samsung Electronics dropped as much as 14% before trimming its loss to 5.2% by the close. Together, the two chipmakers account for more than half of the KOSPI's total market capitalization.

Investors had built substantial positions in both companies during the artificial intelligence investment boom, with robust demand for advanced memory chips — particularly high-bandwidth memory used in AI accelerators — underpinning share prices throughout the year. Global cloud providers and tech platforms had committed hundreds of billions of dollars to AI infrastructure, driving outsized demand for the memory chips that SK Hynix and Samsung supply. However, the crowded trade left the market exposed once investors began de-risking. The unwinding accelerated as falling prices triggered cascading margin calls and forced sales.

Japan and Taiwan Track Regional Downturn

Taiwan's market also weakened as investors unloaded major semiconductor holdings. TSMC, the world's largest contract chipmaker, declined 3.5% in Taipei trading. The broader Taiwanese market lost approximately 3% during the session, with estimated value erosion of $110 billion.

Japan's Nikkei followed the regional trend lower, with technology and semiconductor shares dragging the benchmark down roughly 1.5% and wiping out an estimated $105 billion in value. Investors reduced exposure to companies tied to global chip demand and AI-related capital expenditure.

The three markets represent complementary links in the global semiconductor supply chain: South Korea in memory chips, Taiwan in contract manufacturing, and Japan in semiconductor equipment and materials. Weakness in one segment can signal broader demand uncertainty across the chain. Currency fluctuations also affected dollar-denominated loss estimates as local indexes recovered from intraday lows.

Leverage and Valuation Pressures Amplify Rout

Leveraged retail products amplified South Korea's market decline. Single-stock leveraged ETFs, which magnify the daily price movements of Samsung and SK Hynix shares, caused losses to compound rapidly when underlying stocks fell sharply.

South Korean authorities acknowledged that these products contributed to heightened volatility. Finance Minister Koo Yun-cheol and Financial Services Commission Chairman Lee Eog-weon issued apologies for the policy permitting the products, stating that officials had not adequately assessed the risks before granting approval.

The government had previously announced measures targeting single-stock leveraged ETFs and exchange-traded notes on July 16, including stronger investor protections, tighter product-management requirements, and restrictions on new offerings from firms failing to meet the standards.

President Lee Jae Myung also directed regulators to prepare additional measures addressing the products' impact on market stability.

Leveraged ETFs were not the sole driver of the sell-off. Investors also reacted to elevated technology valuations, rising borrowing costs, and growing doubts about returns on large-scale AI investments. Semiconductor stocks have historically been sensitive to shifts in the demand cycle, and the sector's rapid run-up during the AI buildout left valuations particularly vulnerable to any change in sentiment.

KOSPI Holds Year-to-Date Gains Despite Pullback

Notwithstanding the recent retreat, the KOSPI remained substantially higher for the year in U.S. dollar terms. Before the reversal, the index had ranked among the strongest-performing major equity benchmarks globally, propelled by Samsung, SK Hynix, and broader expectations for sustained AI-related spending.

The latest decline represents a sharp valuation correction rather than a full reversal of the year's preceding gains. South Korea remained the epicenter of the regional sell-off, though parallel declines in Taiwan and Japan confirmed that concerns about semiconductor valuations had permeated across Asia.