A semiconductor device includes a substrate having an active region, a gate structure intersecting the active region and extending in a first direction parallel to a top surface of the substrate, a first source/drain region and a second source/drain region disposed in the active region at both sides of the gate structure, respectively, and a first modified contact and a second modified contact in contact with the first source/drain region and the second source/drain region, respectively. The distance between the gate structure and the first modified contact is smaller than the distance between the gate structure and the second modified contact.