KOSPI Slumps to 6,666 as Oil Prices Surge and Treasury Yields Soar

The KOSPI index plummeted to 6,666 on Thursday as rising oil prices and increasing U.S. Treasury yields drove foreign investors out of the market.

The index opened at 6,625.47, down 210.33 points (3.08%), but recovered some losses in early trading before declining over 2% for the day.

The decline was triggered by additional U.S. airstrikes on Iran, which heightened concerns about crude supply disruptions through the Strait of Hormuz and pushed October-delivery West Texas Intermediate crude futures up 5.2% to $90.22 per barrel.

The surge in oil prices spilled over into inflation concerns, causing global bond yields to rise. The U.S. 10-year Treasury yield reached 4.8%, its highest since early 2025, while the 30-year yield climbed to 5.272%, approaching its highest level since 2007.

In contrast, Other Corporations, buoyed by Samsung Electronics and SK Hynix share buybacks, stood alone as buyers, propping up the index's downside with net buying of ₩290.6 billion (approximately $212.4 million).