Top 10 Market Cap Companies in the U.S. Stock Market Over a Decade 2016: All 10 were in the S&P 500, with 5 in the Nasdaq 100 2026: 9 in the S&P 500 (TSMC can't be included), all 10 in the Nasdaq 100 Ten years ago, the largest U.S. companies spanned industries like tech, energy, finance, healthcare, and industrials. Ten years later, the largest U.S. companies are almost entirely tech-focused. The core assets of the U.S. stock market have shifted from 'American economy' to 'American tech.' Tonight, SpaceX makes a strong debut, with big players like OpenAI and Anthropic still to come. The reshuffling of the U.S. stock market's Top 10 will only get more intense.