A semiconductor device includes a plurality of active fins on a substrate, a gate electrode intersecting the plurality of active fins, and a source/drain region on the plurality of active fins, extending on a first side and a second side of the gate electrode. The source/drain region includes lower epitaxial layers on ones of the plurality of active fins. The lower epitaxial layers include germanium (Ge) having a first concentration. An upper epitaxial layer is on the lower epitaxial layers, and includes germanium (Ge) having a second concentration that is higher than the first concentration. The lower epitaxial layers have convex upper surfaces, and are connected to each other between the active fins.