Provided is a semiconductor device which includes a substrate including a first region and a second region different from the first region, a first active pattern provided on the substrate in the first region, a second active pattern provided on the substrate in the second region, a first gate structure crossing over the first active pattern and a second gate structure crossing over the second active pattern, first source/drain regions disposed on the first active pattern at opposite sides of the first gate structure, second source/drain regions disposed on the second active pattern at opposite sides of the second gate structure, and auxiliary spacers disposed in the first region to cover a lower portion of each of the first source/drain regions.