The KOSPI index broke above 7,500 during trading on Wednesday, but later swung between sharp falls and rebounds before ending a rollercoaster session near 7,490. Foreigners, in particular, stepped up intraday volatility by posting net sales of more than 7 trillion won.

The KOSPI closed up 105.49 points, or 1.43 percent, at 7,490.05. It opened up 114.51 points, or 1.55 percent, at 7,499.07. It again set a fresh intraday record, surpassing the previous day's all-time high of 7,426.60.

By investor type, retail investors were net buyers of 5.9914 trillion won and institutions were net buyers of 1.0984 trillion won. Foreigners, meanwhile, were net sellers of 7.154 trillion won and moved to take profits after net buying more than 6 trillion won over the previous two days.

Top market-cap stocks were mostly higher. Samsung Electronics rose 2.07 percent to 271,500 won, and SK Hynix gained 3.31 percent to 1,654,000 won.

Elsewhere, SK Square rose 0.92 percent, Hyundai Motor gained 4.00 percent, LG Energy Solution added 0.21 percent, Doosan Enerbility climbed 7.40 percent, HD Hyundai Heavy Industries rose 6.94 percent, and Samsung Electro-Mechanics ended up 0.55 percent.

Samsung Biologics fell 0.81 percent.

The KOSDAQ ended down 10.99 points, or 0.91 percent, at 1,199.18, falling below the 1,200 level.

In the Seoul foreign exchange market, the won ended at 1,452.70 per dollar, down 3.70 won.