Demand for AI infrastructure continues to rise, further concentrating the gains in the US stock market on a few sectors. Latest data shows that semiconductor stocks now account for 18.8% of the S&P 500's market capitalization, a record high and significantly higher than in 2022.

The SOX index has surged 546% in three years.

This expansion coincided with a significant rise in the Philadelphia Semiconductor Index (SOX). Data shows that the SOX index has increased by 546% since 2022, primarily driven by continued market investment in infrastructure such as AI chips, servers, and data centers.

The semiconductor sector now accounts for more than three times the weight of the S&P 500 as it did in 2022. This increased sector concentration means that the index's performance is becoming increasingly reliant on a few large technology and chip companies.

The weighting is higher than during the dot-com bubble period.

This change has attracted attention because semiconductor companies now account for a larger share of the S&P 500 than during the dot-com bubble. Meanwhile, the "Big Seven" US stocks currently account for approximately 33% of the total market capitalization of the S&P 500.

This indicates that the index's rise is increasingly driven by a few leading companies, rather than by broader industry confluence. For funds passively tracking the S&P 500, this structure also amplifies their exposure to leading technology stocks.

The year-to-date gains have mainly come from AI and energy.

Apollo's statistics also show that since January of this year, almost all of the S&P 500's gains have come from AI and energy-related stocks. In other words, the current upward momentum in US stocks is increasingly concentrated in a few sectors that are clearly benefiting.

From a market structure perspective, the record high weighting of semiconductors not only reflects the continued enthusiasm for AI investment, but also shows that the S&P 500 is becoming increasingly reliant on a few sectors.