A semiconductor device comprising a plurality of active patterns on a substrate. The semiconductor device may include a device isolation layer defining the plurality of active patterns, a gate electrode extending across the plurality of active patterns, and a source/drain pattern on the active patterns. The plurality of active patterns may comprise a first active pattern and a second active pattern. The source/drain pattern comprises a first part on the first active pattern, a second part on the second active pattern, and a third part extending from the first part and along an upper portion of the first active pattern. The device isolation layer comprises a first outer segment on a sidewall of the first active pattern below the source/drain pattern. A lowermost level of a bottom surface of the third part may be lower than an uppermost level of a top surface of the first outer segment.