Abstract: A device includes: a substrate having a semiconductor fin; a stack of semiconductor channels on the substrate and positioned over the fin; a gate structure wrapping around the semiconductor channels; a source/drain abutting the semiconductor channels; an inner spacer positioned between the stack of semiconductor channels and the fin; an undoped semiconductor layer vertically adjacent the source/drain and laterally adjacent the fin; and an isolation structure that laterally surrounds the undoped semiconductor layer, the isolation structure being between the source/drain and the inner spacer.