In an exemplary aspect, the present disclosure is directed to a device. The device includes a fin-shaped structure extending lengthwise along a first direction. The fin-shaped structure includes a stack of semiconductor layers arranged one over another along a second direction perpendicular to the first direction. The device also includes a first source/drain feature of a first dopant type on the fin-shaped structure and spaced away from the stack of semiconductor layers. The device further includes a second source/drain feature of a second dopant type on the fin-shaped structure over the first source/drain feature along the second direction and connected to the stack of semiconductor layers. The second dopant type is different from the first dopant type. Furthermore, the device additionally includes an isolation feature interposing between the first source/drain feature and the second source/drain features.