The present disclosure describes a semiconductor device having facet-free epitaxial structures with a substantially uniform thickness. The semiconductor device includes a fin structure on a substrate. The fin structure includes a fin bottom portion and a fin top portion. A top surface of the fin bottom portion is wider than a bottom surface of the fin top portion. The semiconductor device further includes a dielectric layer on the fin top portion, an amorphous layer on the dielectric layer, and an epitaxial layer. The epitaxial layer is on a top surface of the amorphous layer, sidewall surfaces of the amorphous layer, the dielectric layer, the fin top portion, and the top surface of the fin bottom portion.