Nearly 45% of S&P 500 tied to AI as megacaps lead

Nearly 45% of the S&P 500’s market capitalization is tied to companies linked to artificial intelligence, driven by semiconductor, data center and energy firms that supply AI infrastructure. Nvidia held about a 7% weight in the index as of March 30, 2026, and the five largest AI-related companies together account for roughly 30% of the S&P 500.

Data center construction and AI capital expenditure have scaled rapidly. Projections show AI-related infrastructure spending is on track to reach about 2% of U.S. gross domestic product by late 2026. Goldman Sachs projects that AI infrastructure investments will contribute about 40% of S&P 500 earnings growth in 2026. Capital Economics estimates that, without the AI-related lift, the index would trade roughly 25% lower.

The top 20 AI-linked names make up nearly half of the index’s weight, a concentration that matches or exceeds levels seen at the 2000 dot-com peak. Since the 2022 launch of ChatGPT, stocks tied to AI infrastructure have risen roughly 200%, while the remaining companies in the S&P 500 averaged about 27% gains over the same period.

Hyperscale cloud providers are central to the spending surge. The four largest — Amazon, Alphabet, Meta and Microsoft — are projected to spend between $645 billion and $700 billion on AI infrastructure in 2026. That spending is supporting firms that supply chips, servers, networking equipment and power capacity. Companies added to the S&P 500 on March 3, 2026 with ties to that buildout include Lumentum, Vertiv Holdings and Coherent.

Energy and industrial companies have also registered gains because modern data centers require significant power and specialized equipment. Notable names linked to the AI infrastructure boom in 2025 and early 2026 include GE Vernova, NRG Energy, Seagate Technology, Super Micro Computer and Palantir Technologies.

Market participants are watching whether the large capital expenditures are translating into measurable revenue growth and margin expansion. Analysts at Morgan Stanley and Goldman Sachs recommend focusing on companies that adopt AI with clear pricing power and on infrastructure firms that connect to manufacturing and energy rather than relying on broad technology exposure.

Higher correlation across sectors tied to the data center buildout has affected index diversification. A slowdown in AI capital expenditure would change the market’s revenue and earnings outlook for the firms most connected to that spending.