South Korea stocks plunge as margin calls add to market stress

South Korea’s KOSPI has recorded a sharp market decline after emergency circuit breakers halted trading twice in one week.

The benchmark index fell 13% across eight trading days as margin calls and hedging demand rose. The selloff has also hit Asian markets, while Samsung and SK Hynix concentration adds pressure.

KOSPI triggers rare emergency halts

According to Bull Theory, the KOSPI triggered full circuit breakers on June 8 and June 10. Each halt stopped trading for 20 minutes as selling pressure moved across the market. The KOSPI has recorded only ten full circuit breakers in its history. Two of those emergency halts occurred in the same week.

The index fell 13% in eight trading days, according to the provided market data. The pace of the decline brought renewed focus to South Korea’s equity market structure. The KOSPI 200 put-call ratio reached 2.5, its highest level in five years. The reading means traders bought 2.5 downside contracts for every upside contract.

Bull Theory said that ratio has appeared only twice in 20 years. It appeared in July 2007 before a 17% decline and in January 2021 before a 5% drop. Institutions have moved toward downside protection instead of dip buying, according to the market data. A sidecar also stopped program trading for five minutes on June 5.

Margin calls hit retail traders

The market fall has increased pressure on retail traders with large margin positions. Global Markets Investor said forced stock sales from margin calls reached about 300 billion won. The figure equals about $197 million, based on the provided conversion. Global Markets Investor described it as the largest reading on record.

Retail margin debt now stands near 38 trillion won, or about $24.9 billion. The high debt level leaves leveraged traders exposed during fast market moves. Recent KOSPI moves show the scale of the volatility. The index fell 8.3% on Monday, then rebounded 8.2% on Tuesday.

The index then dropped 4.5% on Wednesday, according to the provided data. Program trading stopped on Monday and Wednesday to slow automated selling. The KOSPI 200 volatility index moved above 90 on Tuesday. The reading reached its highest level on record.

Samsung and SK Hynix concentration adds risk

Samsung and SK Hynix now account for more than 50% of the KOSPI’s total weighting. Their size gives both companies heavy influence over the benchmark index. The two chip stocks also account for nearly 75% of the KOSPI’s 2026 gains. The data shows that a small group drove most of the index advance.

This concentration leaves the index exposed when either company faces selling pressure. The structure also limits support from weaker parts of the market. The turmoil has spread across Asia and removed hundreds of billions from regional markets. The provided data links the move to South Korea’s sharp equity losses.

Institutional hedging, retail liquidations, and index concentration now shape the current market stress. Each factor has added pressure during the latest KOSPI decline. The most recent data showed two circuit breakers in one week and retail margin debt near record levels. Samsung and SK Hynix remained central to the index’s 2026 performance.