Semiconductor devices and methods of forming the same are provided. A semiconductor device according to the present disclosure includes first channel members over a first backside dielectric feature, second channel members over a second backside dielectric feature, a first epitaxial feature abutting the first channel members and over the first backside dielectric feature, a second epitaxial feature abutting the second channel members and over the second backside dielectric feature, a first gate structure wrapping around each of the first channel members, a second gate structure wrapping around each of the second channel members, and an isolation feature laterally stacked between the first backside dielectric feature and the second backside dielectric feature. A bottommost portion of the isolation feature is below bottom surfaces of the first and second gate structures, and a topmost portion of the isolation feature is above top surfaces of the first and second gate structures.