KOSPI-Nasdaq 100 Correlation Hits 5-Year High at 0.50 as AI Drives South Korea-U.S. Market Synchronization

According to CNBC citing research from Resilient Research, the 60-day correlation coefficient between South Korea's KOSPI index and the U.S. Nasdaq-100 reached approximately 0.50 on July 27, marking the highest level since 2021. The surge reflects growing AI investment interconnection, as Samsung Electronics and SK Hynix—which together account for over half of KOSPI's market capitalization—have become core suppliers in the AI server DRAM supply chain, amplifying the impact of U.S. big tech AI spending on both markets simultaneously.

According to Futurum Group, data center demand's share of global DRAM consumption expanded from roughly 40% in 2025 to over 50% in 2026. The heightened synchronization reduces diversification benefits investors historically gained by holding both Korean and U.S. equities. Experts warned that if U.S. big tech capital expenditure slows, KOSPI could face sharper downside than other markets. Japan's Nikkei newspaper reported on July 28 that increased trading in leveraged single-stock ETFs tracking Samsung and SK Hynix has amplified volatility in Japanese semiconductor stocks, including Kioxia.