Gate-all-around (GAA) devices and methods for fabricating such are disclosed herein. An exemplary GAA device includes a first semiconductor layer disposed over a substrate. A gate structure is disposed over and wraps a portion of the first semiconductor layer, such that the gate structure separates a source region of the first semiconductor layer and a drain region of the first semiconductor layer. A channel region of the first semiconductor layer is defined between the source region and the drain region. A dielectric layer is disposed adjacent to the first semiconductor layer, where the dielectric layer extends along an entirety of the source region of the first semiconductor layer and an entirety of the drain region of the first semiconductor layer. A second semiconductor layer disposed over the source region of the first semiconductor layer, the drain region of the first semiconductor layer, and the dielectric layer.