South Korea's stock market has become the world's most concentrated major equity benchmark, with two chipmakers accounting for 60% of the KOSPI's market capitalization — a structural risk that Goldman Sachs warns could trigger $2 billion in forced foreign selling.
The KOSPI's reliance on Samsung Electronics Co. and SK Hynix Inc. has reached a record 60% of the index's weight, up from about 40% two years ago, as the AI chip boom drove both stocks to roughly triple and quadruple in value this year. Goldman Sachs analysts Timothy Moe and John Kwon warned that each additional percentage point of combined weight could force foreign investors subject to US diversification rules to sell about $2 billion from the Korean market.
"The combination of leveraged ETF inflows, active options trading, and retail margin debt has created a structural fragility where daily price swings far exceed what fundamentals would justify," Moe and Kwon wrote in a note, according to the Wall Street Journal.
The KOSPI has already triggered five circuit breakers this year, including a 10% single-day crash last Tuesday and a 5.81% drop on Friday that halted trading for 20 minutes. Samsung fell 5.30% to 339,500 won and SK Hynix dropped 8.36% to 2.673 million won in Friday's session alone. Foreign investors dumped a net 4.62 trillion won ($3.4 billion) while retail buyers absorbed 8.19 trillion won ($6 billion) in the opposite direction. The MSCI Korea index has posted daily moves exceeding 5% on 20% of trading days in 2026, compared with just 0.8% in 2025, according to Julius Baer.
The concentration is extreme by global standards — Nvidia Corp. and Apple Inc. together account for about 20% of the Nasdaq, while Toyota Motor Corp. and Kioxia Holdings Corp. represent less than 10% of Japan's Nikkei 225. Any pullback in global AI spending could trigger cascading forced liquidations in Seoul, analysts warned, as margin debt and leveraged products amplify downside moves.
The $2 Billion Trigger Point
Goldman's analysis pinpoints a precise risk threshold. Under the US Investment Company Act, diversified funds face limits on concentrated holdings. If Samsung and SK Hynix's combined KOSPI weight rises another percentage point, funds subject to those rules would need to rebalance, generating about $2 billion in selling pressure, the analysts calculated.
Morningstar analyst Jing Jie Yu highlighted that retail margin borrowing in both stocks has climbed to all-time highs. "That massively amplifies price volatility — both on the way up and on the way down, as margin calls force selling," Yu said.
Regulators Scramble as Volatility Intensifies
The Korea Exchange has activated its 20-minute circuit breaker five times in 2026, including twice last week. Plans to launch weekly options on four large-cap stocks including Samsung and SK Hynix were postponed because of excessive volatility.
Financial Supervisory Service Governor Lee Chan-jin publicly expressed regret over failing to block the listing of single-stock leveraged ETFs in May. "I should have gone all out to stop it. I deeply regret it," Lee said.
The warning from Goldman comes as Apple Inc. raised product prices citing higher memory costs, a move that helped trigger Friday's selloff. With AI infrastructure spending showing no signs of slowing, the structural risk embedded in Korea's market may persist until either the weight normalizes or regulators impose stricter concentration limits.
This article is for informational purposes only and does not constitute investment advice.
