A semiconductor device includes an active pattern having sidewalls defined by a device isolation pattern disposed on a substrate and an upper portion protruding from a top surface of the device isolation pattern, a liner insulating layer on the sidewalls of the active pattern, a gate structure on the active pattern, and source/drain regions at both sides of the gate structure. The liner insulating layer includes a first liner insulating layer and a second liner insulating layer having a top surface higher than a top surface of the first liner insulating layer. Each of the source/drain regions includes a first portion defined by the second liner insulating layer, and a second portion protruding upward from the second liner insulating layer and covering the top surface of the first liner insulating layer.