A device comprises insulation regions disposed in a substrate and a semiconductor fin extending above top surfaces of the insulation regions. The semiconductor fin comprises a first material. A semiconductor region comprising a second material extends from a first side of the semiconductor fin over a top of the fin to a second side of the fin. A strain buffer layer is disposed between, and contacts, the semiconductor fin and the semiconductor region. The strain buffer layer comprises an oxide, and a bottommost surface of the strain buffer layer is vertically spaced apart from the top surfaces of the insulation regions.