The S&P 500's top ten stocks now make up about 39% of the index's total value, the most concentrated the market has been since 1965. Nearly all of those top holdings are tied to AI development, echoing the run-up before the dot-com bust, though the index has historically recovered from steep pullbacks.
The S&P 500 is valued at around $70.4 trillion, and its top ten stocks alone account for $27.4 trillion of that, or roughly 39%. Nvidia, Apple, Alphabet, Microsoft, Amazon, Meta Platforms, Broadcom, Tesla, Micron Technology, and Berkshire Hathaway make up that group, in that order. The last time the index was this concentrated was in 1965, according to S&P Global data, but back then the top names spanned varied industries rather than a single theme.
AI spending dominates the index's top holdings
Nearly all of the S&P 500's largest stocks are heavily or tangentially focused on AI. Amazon, Meta, Microsoft, and Alphabet together spent over $300 billion building data centers in the first half of 2026, and those four are expected to account for nearly half of global AI infrastructure spending this year. Goldman Sachs estimates hyperscalers will need at least $300 billion in AI revenue over the next few years just to break even, and $1 trillion a year for healthy margins. It's still anyone's guess whether that spending pays off, but a shortfall could ripple across the broader market.
History points to the dot-com bubble
The last comparable spike in concentration came during the dot-com bubble, when the top ten holdings climbed from 17% of the index's value in June 1994 to more than 26% by June 2000. Since the current bull market began in late 2022, concentration has jumped again, from around 26% to 39%.
At the same time, the S&P 500's Shiller CAPE ratio, a valuation measure, sits above 40, approaching the dot-com-era record of 44. When the tech sector collapsed after that bubble burst, the S&P 500 lost nearly half its value over the following two years.
No two bear markets are identical, and even the strongest indicators can't predict the future. Still, since early 1999, when valuations first began climbing toward bubble levels, the index has gone on to earn total returns of nearly 1,000%.
Source: The Motley Fool
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