South Korea's KOSPI became unusually volatile as gains and losses were concentrated in Samsung Electronics and SK Hynix, while foreign selling and leveraged investment amplified market swings, the Bank of Korea said. The central bank found that the two chipmakers accounted for 99.0% of the index's rise from 8,000 to 9,000 and 69.3% of its subsequent decline from around 9,100 to 5,500. Daily KOSPI volatility averaged 4.1% from January through July, the highest among the 30 largest equity markets by capitalization and above levels recorded during prior crisis periods. The BOK said strong expectations for artificial intelligence and semiconductor demand concentrated investor exposure in memory-chip stocks, leaving the wider market more vulnerable to changes in the industry outlook. It also cited foreign investors' profit-taking, portfolio rebalancing, margin-funded trading and leveraged ETFs as forces that widened price moves. Leveraged positions have been largely unwound and volatility has eased, but the central bank said sector concentration remains and called for closer oversight of leveraged ETFs and borrowing-funded share purchases, alongside longer-term efforts to broaden the investor base.