A semiconductor structure and a method of forming the same are provided. In an embodiment, a semiconductor structure includes an epitaxial source feature and an epitaxial drain feature, a vertical stack of channel members disposed over a backside dielectric layer, the vertical stack of channel members extending between the epitaxial source feature and the epitaxial drain feature along a direction, a gate structure wrapping around each of the vertical stack of channel members, and a backside source contact disposed in the backside dielectric layer. The backside source contact includes a top portion adjacent the epitaxial source feature and a bottom portion away from the epitaxial source feature. The top portion and the bottom portion includes a step width change along the direction.