South Korea’s benchmark KOSPI index doubled in the first half of 2026 on AI memory chip demand before erasing approximately $2.18 trillion in market value over two sessions in late July, posting its steepest monthly decline on record. Samsung Electronics and SK Hynix together account for over 50% of the KOSPI’s total market capitalization, turning any earnings miss into a systemic event for the entire market. On July 30, the index surged 17.9% in a single day, one of the largest single-session rebounds in any major market’s history. Margin debt had reached all-time highs and leveraged ETF products amplified the selloff during margin calls. The KOSPI episode illustrates concentration risk and the market’s sensitivity to hyperscaler AI capital expenditure expectations.
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