A semiconductor device may include a first active fin, a plurality of second active fins, a first source/drain layer structure, and a second source/drain layer structure. The first active fin may be on a first region of a substrate. The second active fins may be on a second region of the substrate. The first and second gate structures may be on the first and second active fins, respectively. The first source/drain layer structure may be on a portion of the first active fin that is adjacent to the first gate structure. The second source/drain layer structure may commonly contact upper surfaces of the second active fins adjacent to the second gate structure. A top surface of the second source/drain layer structure may be further from the surface of the substrate than a top surface of the first source/drain layer structure is to the surface of the substrate.