Semiconductor devices and methods are provided. An exemplary method according to the present disclosure includes forming a semiconductor fin over a substrate, forming an integral dielectric layer over the substrate, wherein the dielectric layer includes a first portion extending along a sidewall surface of the semiconductor fin and a second portion disposed over the semiconductor fin, a thickness of the second portion of the dielectric layer is greater than a thickness of the first portion of the dielectric layer, forming a dummy gate electrode layer over the substrate, patterning the dielectric layer and the dummy gate electrode layer to form a dummy gate structure over a channel region of the semiconductor fin, forming source/drain features coupled to the channel region of the semiconductor fin and adjacent to the dummy gate structure, and replacing the dummy gate structure with a gate stack.