A semiconductor device includes a substrate, a first region and a second region. Each of the first region and second region includes a trench, an epitaxial layer including a source/drain having a first part and a second part, the first part extending from a top surface of the substrate to a top surface of the source/drain and the second part extending from the top surface of the substrate to a bottom surface of the source/drain in the trench. The cross-sectional shape of the first part of the source/drain of the first region is the same as the cross-sectional shape of the first part of the source/drain of the second region. The cross-sectional shape of the second past of the source/drain of the find region is different from the cross-sectional shape of the second part of the source/drain of the second region.