The present disclosure provides a semiconductor device and a method of manufacturing the semiconductor device. The semiconductor device includes channel members vertically stacked above a substrate, a gate structure engaging the channel members, a gate sidewall spacer disposed on a sidewall of the gate structure, an epitaxial feature abutting end portions of the channel members, and inner spacers interposing the gate structure and the epitaxial feature. The end portion of at least one of the channel members includes a first dopant. A concentration of the first dopant in the end portion of the at least one of the channel members is higher than in a center portion of the at least one of the channel members. The concentration of the first dopant in the end portion of the at least one of the channel members is higher than in an outer portion of the epitaxial feature.