South Korea's KOSPI rose more than 4 percent on Sept. 7, lifted by sharp gains in heavyweight chip stocks such as Samsung Electronics and SK Hynix, climbing to just below the 7,000 level. With expectations rising for increased AI infrastructure investment and expanding demand for memory semiconductors following the release of OpenAI's new artificial intelligence (AI) model, foreigners and institutions moved to make large-scale purchases.

The KOSPI closed up 308.18 points, or 4.61 percent, at 6,995.39. It opened at 6,910.78, up 223.57 points, or 3.34 percent, from the previous session, and climbed as high as 6,995.40 before ending near 7,000.

In the main board market, foreigners were net buyers of 2.5533 trillion won and institutions were net buyers of 2.6327 trillion won. Retail investors were net sellers of 6.8212 trillion won.

Chip stocks led the index higher. Samsung Electronics ended up 5.68 percent at 270,000 won and SK Hynix jumped 8.26 percent to 1,783,000 won.

Other top market-cap stocks also rose, including SK Square, up 8.07 percent, Samsung Electro-Mechanics, up 3.78 percent, Samsung C&T, up 4.50 percent, Samsung Life Insurance, up 4.87 percent, Hyundai Motor, up 2.48 percent, KB Financial Group, up 2.27 percent, Samsung Biologics, up 1.31 percent, and LG Energy Solution, up 1.12 percent.

The Kosdaq also ended higher. The index rose 8.69 points, or 1.07 percent, to 822.19.

In the Seoul foreign exchange market, the won ended at 1,341.10 per dollar, up 8.40 won, or 0.62 percent, from the previous session.

Sentiment for domestic chip investment is seen as having improved as expectations grew for increased AI infrastructure investment and higher memory demand after OpenAI released its new AI model, Astra. In U.S. markets, semiconductor stocks also outperformed the broader market, with the Philadelphia Semiconductor Index rising 3.4 percent on Sept. 4 local time.