A semiconductor device includes a substrate including an upper surface and a lower surface that are opposite to each other in a first direction, an active pattern which is on the upper surface of the substrate and extends in a second direction, a gate electrode which is on the active pattern and extends in a third direction, a first source/drain pattern which is connected to the active pattern on the upper surface of the substrate, and includes a lower epitaxial region and an upper epitaxial region, the upper epitaxial region including an epitaxial recess, and the lower epitaxial region being inside the epitaxial recess, a first source/drain contact, which is connected to the first source/drain pattern and extends into the substrate, and a contact silicide layer, which is between the first source/drain contact and the first source/drain pattern and contacts the lower epitaxial region.