S&P 500 Posts Best May Since 1950s as AI Rally Defies Sell-in-May Adage

The S&P 500 rose more than 5% in May, its strongest May performance in over 70 years, as an artificial-intelligence boom and tech-stock surge overpowered the traditional “Sell in May and go away” strategy. The benchmark recouped all of its spring decline. The technology-heavy Nasdaq Composite gained 8.2% for the month, while the information technology sector soared 18%. Micron Technology (MU) shares skyrocketed 78%, briefly breaching a $1 trillion market capitalization, and Advanced Micro Devices (AMD) advanced 46%. The Philadelphia Semiconductor Index rose over 22% from the end of April. S&P 500 first-quarter earnings jumped 29% from a year earlier, the strongest growth in at least three years, according to LSEG. Some strategists flagged caution, noting that parabolic chip-stock gains and elevated valuations could trigger near-term selling, particularly during the lower-volume summer months. But robust AI infrastructure spending and a resilient U.S. labor market are expected to sustain the longer-term uptrend.