US retail investors recorded about $9.1 billion in net stock purchases through Citadel Securities’ platform last week, the strongest weekly total in nearly 15 years. Semiconductor stocks accounted for about $2.6 billion, their third-highest weekly net buying total in the past year, while AI infrastructure-related shares attracted about $2.4 billion. Buying also focused on other artificial intelligence stocks and exchange-traded funds. Scott Rubner, Citadel Securities’ head of equity and equity derivatives strategy, said the figures reflected stronger directional conviction rather than broader trading activity: purchases exceeded sales by 2.7%, placing the weekly imbalance at the 90th percentile of the past year, while overall activity ranked at the 42nd percentile. The buying coincided with record highs for the Nasdaq 100 and S&P 500, as investors weighed AI growth prospects and concerns about a potential bubble. Rubner had said October could offer another opportunity to increase equity allocations as companies report earnings and resume share buybacks.