A semiconductor device includes first and second active patterns on first and second active regions of a substrate, respectively, a pair of first source/drain patterns and a first channel pattern therebetween which are in an upper portion of the first active pattern, a pair of second source/drain patterns and a second channel pattern therebetween which are in an upper portion of the second active pattern, and first and second gate electrodes intersecting the first and second channel patterns, respectively. Each of the first and second gate electrodes includes a first metal pattern adjacent to a corresponding one of the first and second channel patterns. The first and second channel patterns include SiGe. A Ge concentration of the second channel pattern is higher than a Ge concentration of the first channel pattern. A thickness of the first metal pattern of the second gate electrode is greater than a thickness of the first metal pattern of the first gate electrode.