A device includes a substrate, and a first semiconductor channel over the substrate. The first semiconductor channel includes a first nanosheet of a first semiconductor material, a second nanosheet of a second semiconductor material in physical contact with a topside surface of the first nanosheet, and a third nanosheet of the second semiconductor material in physical contact with an underside surface of the first nanosheet. The first gate structure is over and laterally surrounding the first semiconductor channel, and in physical contact with the second nanosheet and the third nanosheet.