The stock market ended May on a historic high. It also ended with a warning sign that echoes the infamous dot-com bubble of the early 21st century.
CNBC reported that only 20 companies in the index also reached their own all-time highs on that session. That narrow participation, Bank of America strategist Michael Hartnett noted, mirrors a striking detail from March 2000, when only 20 stocks hit records at the top of the dot-com bubble.
The parallel does not mean a crash is imminent. It does, however, show how much of the market's latest surge depends on a small group of companies tied to artificial intelligence. According to CNBC, only seven of the 20 S&P 500 companies that hit records last Friday were not directly linked to AI.
The rest were involved in chips, data centers, hardware and companies seen as essential to the next phase of computing and the industry. The Nasdaq Composite jumped 25% across April and May, its best two-month stretch since late 2002, while the S&P 500 gained about 16% in the same period.
CNBC reported that Micron Technology rose 88% in May, Advanced Micro Devices climbed 46%, Samsung gained 44%, and SK Hynix surged 81%. Micron crossed a $1 trillion valuation after a sharp rally fueled by optimism over memory demand.
Axios also reported that the AI stock boom gained momentum in May, with legacy technology names such as Cisco, Hewlett-Packard Enterprise, and Micron posting major gains as investors chased exposure to the infrastructure behind artificial intelligence. That is exactly what worries some strategists.
A healthy bull market usually broadens over time, with gains spreading across industries. A narrow rally can be fragile because indexes may continue rising even as many individual stocks fall behind. CNBC cited advance-decline lines, which track how many stocks are rising versus falling, as one sign of internal weakness.
Ari Wald of Oppenheimer wrote in a May 23 technical analysis that "internals have lagged since the initial April surge." BCA Research also warned that only about 55% of S&P 500 stocks were trading above their 200-day moving average as of May 20, calling poor breadth a sign of market vulnerability.
The dot-com comparison is uncomfortable because the late 1990s also featured a transformative technology, soaring valuations, and investor belief that a new era had arrived. Some companies from that period eventually became giants.
Many others disappeared after the bubble burst. Hartnett, according to CNBC, told clients that the speculative phase may not be over, but he believes central banks and rising interest rates could eventually end it. His suggested "post-bubble" roadmap favors long bonds and defensive sectors that underperformed during the final months of the rally.
Still, not everyone sees only danger. The Wall Street Journal reported that the S&P 500's 16% gain over April and May was one of its strongest two-month performances since 1950, and that similar rallies historically were followed by additional gains over the next six months.
