A semiconductor device includes a device isolation layer on a substrate, a first active pattern defined by the device isolation layer, and source/drain regions. The first active pattern extends in a first direction and includes a channel region between a pair of recesses formed at an upper portion of the first active pattern. The source/drain regions fill the pair of recesses in the first active pattern. Each of the source/drain regions include a first semiconductor pattern in the recess and a second semiconductor pattern on the first semiconductor pattern. The source/drain region have an upper portion whose width is less than a width of its lower portion. The second semiconductor pattern has an upper portion whose width is less than a width of its lower portion. The upper portion of the second semiconductor pattern is positioned higher than a top surface of the channel region.