Philadelphia Semiconductor Index Plunges 11.2%, Worst One-Day Drop Since March 2020

The scale of the move—the worst since March 2020—matters more than the absence of a stated catalyst. It signals that semiconductor equities, the market's AI-era bellwether, remain prone to violent, correlated drawdowns when sentiment shifts, and the lack of an obvious trigger leaves the selloff open to competing narratives. Given the sector's outsized weight in index performance, whether the move proves a one-day repricing or the start of a broader de-risking is the open question worth watching.