Seldom has market sentiment shifted so abruptly. South Korea's KOSPI index plunged 10.8% on July 28, closing at 6,023.66. The precipitous decline triggered the index's eighth circuit breaker of 2026, halting all trading for twenty minutes. Samsung Electronics and SK Hynix, which together constitute nearly half of the benchmark's market capitalization, bore the brunt of the rout.
Samsung recorded its worst single-day loss in almost two decades, falling 13.4%. SK Hynix tumbled 14.7%, amplifying the sell-off across the broader market. The catalyst was a report that a Chinese state-backed firm had begun mass-producing deep ultraviolet lithography machines. This development threatened to erode the competitive moat long enjoyed by established semiconductor equipment makers.
The reversal is particularly striking given the KOSPI's remarkable trajectory earlier this year. The index had peaked at approximately 9,114 in June, propelled by insatiable demand for AI-related memory chips. By late July, however, cumulative losses for the month had approached 23%, erasing roughly 250 trillion won in value. Analysts characterized the correction as a fundamental reassessment of AI infrastructure valuations rather than a deterioration in underlying demand.
The contagion was not confined to Seoul. ASML shares fell 8.5% in Amsterdam, while Japan's Kioxia Holdings slumped 18.3%. Nasdaq futures also declined, reflecting heightened scepticism about the sustainability of AI capital expenditure. Investors worldwide appeared to be rotating out of high-valuation technology assets amid weakening sentiment and geopolitical uncertainty.
What distinguishes this episode from prior corrections is its structural dimension. China's advances in chipmaking equipment challenge the assumption that export controls would indefinitely preserve Western technological supremacy. Should Chinese manufacturers achieve scale in DUV lithography, the pricing power of established players could diminish considerably. For investors, the lesson is unequivocal: concentrated exposure to a single thematic trade amplifies both upside potential and downside risk.
