Kospi's 105% Rally Falters as Breadth Concerns Intensify

South Korea's Stock Market Shows Signs of Strain

South Korea's $4.9 trillion stock market is beginning to exhibit signs of strain after a remarkable year-long rally. The Kospi has surged 105% this year, but when the benchmark reached a record high on Tuesday, only 2.6% of stocks reached their 52-week highs, while 31% slid to their 52-week lows. This uneven distribution of gains is concentrated in a few heavyweights, including Samsung Electronics Co. and SK Hynix Inc.

Retail participation in the market is also losing steam, with retail investors showing less willingness to commit fresh capital. Brokerage deposits fell to 121 trillion won ($79 billion) by May 22 from 137 trillion won on May 12, according to the Korea Financial Investment Association. Meanwhile, margin balance hit a record 38 trillion won on May 29, up from 27.3 trillion won at the end of 2025, KFIA data show.

Market breadth is the central worry, with Samsung Electronics and SK Hynix accounting for 54% of the Kospi's market weight and roughly half of the gauge's average daily turnover in May, according to Korea Exchange data. Nearly three-quarters of the Kospi's gains this year have come from the two firms.

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The rise of leveraged exchange-traded funds (ETFs), designed to magnify daily moves, may further intensify a reversal, as investors warn that any downturn may accelerate as quickly as the rally.

The current market structure is vulnerable to a downturn as it's dominated by the short gamma in the leveraged ETFs, said Kenny Kim, chief executive officer at Meridian One Asset Management. The setup requires investors to chase rallies with heavy buying when the market rises, but forces them to dump shares when the market falls.

Optimism still dominates in Korea, with appetite for AI-related stocks remaining strong. Wall Street banks remain upbeat on chip earnings, and just this week, Goldman Sachs Group Inc. raised its Kospi target to 12,000 from 9,000. However, another test looms next month, when the central bank is widely expected to raise interest rates, which could dampen liquidity.

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The market is sensitive to bond yields because investments are driven by borrowed money, said Seo Sang-Young, a strategist at Mirae Asset Securities. The Bank of Korea's rate hike in July may exacerbate the situation, leading to a period of increased volatility and consolidation in the market.