A semiconductor device includes an active region defined by a device isolation layer and including first and second sections or regions, a gate electrode extending in a first direction across the active region over a channel between the first region and the second region and including at least one first gate tab protruding in a second direction toward the first region, and first and second contact plugs. The first gate tab covers and extends along a boundary between the active region and the device isolation layer. The first contact plug is disposed over the first region, the second contact plug is disposed over the second region, and the second contact plug has an effective width, as measured in the first direction, greater than that of the first contact plug.