South Korea's KOSPI Plunges 10% on June 23 as U.S. Semiconductor Stocks Fall 7.9%

On June 23, South Korea's KOSPI index plunged 10%, triggering circuit breakers multiple times as semiconductor stocks led the decline. SK Hynix and Samsung Electronics each fell over 10%. The sell-off transmitted to U.S. markets the same day, with the Philadelphia Semiconductor Index declining 7.9%, Micron Technology falling 13%, while the Nasdaq and S&P 500 fell 3.3% and 1.4% respectively, according to market reports.

The downturn was triggered by reports that Nvidia's Rubin chip output would be lower than expected and SK Hynix was slowing HBM4 memory chip expansion. Goldman Sachs characterized the move as a technical adjustment in an already stretched rally rather than a fundamental revaluation of AI infrastructure investments, noting investors were repositioning rather than abandoning the sector entirely. However, analysts flagged persistent structural risks, with BTIG's Jonathan Krinsky stating the semiconductor sector faces 10–15% additional downside risk in the medium term.