S&P 500 breadth narrows as AI-led rally echoes dotcom-era peak

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S&P 500 AI-led rally

Highlights

S&P 500 closes May at a record with only 20 constituents at all-time highs, echoing the concentrated rally pattern seen in March 2000 during the internet bubble.
Semiconductors drive May gains with AMD up 50%, Micron 85%, Samsung 43%, and SK Hynix 81%, highlighting AI-related stocks' central role in the current rally.
Advance-decline lines and 200-day moving averages show weakening breadth, leading strategists like Bank of America's Hartnett to recommend a shift toward long bonds and defensive sectors.

May rally concentration and market signal

As reported by CNBC, the S&P 500 closes at a record on the final trading day of May while only 20 constituents reach their own all-time highs, a market pattern that Bank of America strategist Michael Hartnett says mirrors conditions seen at the top of the internet bubble in March 2000.

In a note at the end of last week, Hartnett says just 20 stocks hit new highs at the peak of the dotcom bubble as well. Of the 20 stocks reaching records on Friday, only seven are not directly tied to the AI theme, underscoring how tightly leadership is concentrated in one part of the market.

Hartnett says the speculative price action is likely not over yet, but he views the latest development as another sign that the rally is nearing its later stages. He argues that central banks and rising interest rates are likely to end the surge and has outlined a post-bubble positioning plan for clients.

Semiconductor surge and broader market risks

The May advance is powered largely by semiconductors, especially memory-chip makers and related names including Micron Technology, Advanced Micro Devices, SK Hynix and Samsung. AMD rises 50% during the month, Micron gains 85%, Samsung climbs 43% and SK Hynix advances 81%, reflecting how strongly investor demand is centered on AI-adjacent companies.

The tech-heavy Nasdaq Composite jumps 25% across April and May, marking its strongest two-month stretch in more than two decades. At the same time, a growing number of strategists and investors warn that a bull market led by too few stocks becomes more vulnerable if participation does not broaden.

Other internal market measures also point to weakening breadth. Advance-decline lines surge at the end of March and then pull back in a bearish signal from mid-April, while only about 55% of S&P 500 companies trade above their 200-day moving average as of May 20, according to BCA Research.

Hartnett advises clients to shift soon toward a more defensive stance. He writes that a post-bubble investor roadmap since 1929 favors long bonds and defensive sectors, or segments of the market that sharply underperform during the final months of a bubble.

In our earlier article on the AI-led rally that carried major U.S. indexes toward record highs into early June, we noted that enthusiasm for artificial intelligence continued to outweigh concerns about oil, geopolitical tensions, and uncertainty around Federal Reserve policy. We also highlighted Nvidia’s central role in the AI trade, alongside the market’s focus on key catalysts such as the U.S. jobs report and its potential impact on rate expectations.

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