U.S. stock-market concentration is less extreme than you think

Research from Morgan Stanley shows that despite popular concern, U.S. equity-market concentration is not unusually high: the top 10 U.S. stocks represent about 33.8% of the market cap of the S&P 500 as of September 2025—placing the U.S. as the fifth-least concentrated among leading markets. Countries such as France, Taiwan and Switzerland exhibit much higher single-stock dominance. Analysts say this may soften corporate-governance and diversification concerns tied to large-cap dominance, though they caution that investor behaviour still underweights international allocation and hidden risks remain.