Semiconductor devices are provided. The semiconductor devices include active fins including a buffer layer disposed on a substrate and a channel layer disposed on the buffer layer and having a first second lattice constant higher than a lattice constant of the buffer layer, a gate structure covering the channel layer and intersecting the active fins, sidewall spacers disposed on both sidewalls of the gate structure, and capping layers disposed to contact lower surfaces of the sidewall spacers and having a width substantially the same as a width of the lower surfaces of the sidewall spacers.