The market capitalization of the S&P 500 (Index: SPX) grew by 13% during the third quarter of 2025, more than double the pace it rose during the preceding quarter.

According to Standard and Poor, the index closed out 2025-Q3 with a market cap of nearly $59.32 trillion. This figure represents an increase of $6.82 trillion from the $52.50 trillion S&P reported at the end of 2025-Q2.

Over 56% of the total gain in the S&P 500's market cap was delivered by its top 10 component stocks. Together, these 10 stocks account for 38.9% of the entire valuation of the index, a record high concentration.

The overall membership of the Top 10 stocks of the S&P 500 is unchanged this quarter, but there have been some changes in the relative rankings of the bottom three stocks of the table.

The following chart shows the relative shares of the top 10 stocks in the S&P 500 at the end of the second quarter of 2025.
 

Here are the approximate market capitalizations of each of the S&P 500's top ten component firms at the end trading on 30 September 2025:

• Nvidia (Nasdaq: NVDA) $4,733,844,220,324 (7.98%)
• Microsoft (Nasdaq: MSFT) $4,003,323,779,663 (6.75%)
• Apple (Nasdaq: AAPL) $3,929,288,628,536 (6.62%)
• Amazon (Nasdaq: AMZN) $2,215,800,814,217 (3.74%)
• Meta Platforms (A) (Nasdaq: META) $1,656,272,653,214 (2.79%)
• Broadcom (Nasdaq: AVGO) $1,613,514,964,354 (2.72%)
• Alphabet (A) (Nasdaq: GOOGL) $1,470,425,649,566 (2.48%)
• Tesla (NYSE: TSLA) $1,297,642,736,446 (2.19%)
• Alphabet (C) (Nasdaq: GOOG) $1,182,620,660,455 (1.99%)
• Berkshire Hathaway (B) (Nasdaq: BRK-B) $958,603,483,954 (1.62%)

One important thing to note is that nine of the top ten stocks within the index have valuations in excess of $1 trillion. Only Berkshire Hathaway falls below that still exclusive club.

The index' top-most valued stock, Nvidia, saw its market cap rise enough to account for 8% of the index by itself. Microsoft saw its share of the index dip by a quarter percent to 6.75%, while Apple's share increased from 5.84% to 6.62%.

The next four firms saw small changes in their individual market capitalizations, with Amazon and Meta Platforms losing some relative share of the index' total valuation and Broadcom and Class A shares of Alphabet gaining.

That brings us to where the rankings changed. Both Tesla and Class C shares of Alphabet moved up one slot to eighth and ninth place respectively, while Berkshire Hathaway dropped two positions into the tenth position.

All ten of the S&P 500's Top 10 stocks grew their market capitalizations during 2025-Q3.

Six months ago, the AI-bubble of the preceding two years had all but deflated, but with Nvidia's surge in valuation during 2025-Q2 and 2025-Q3, it appears to have reinflated and expanded.

References

Standard and Poor. S&P Market Attributes. [Excel Spreadsheet]. 30 September 2025. Accessed 1 October 2025.

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