A semiconductor device including a substrate having a plurality of active fins, each of the plurality of active fins extending in a first direction, first and second gate structures crossing over the plurality of active fins, the first and second gate structures extending in a second direction different from the first direction, the first and second gate structures spaced apart from each other in the first direction, at least one insulating barrier extending in the first direction and between the plurality of active fins, the insulating barrier separating lower portions of the first and second gate structures from each other, and a gate isolation layer connected to a portion of the insulating barrier, the gate isolation unit separating upper portions of the first and second gate structures from each other may be provided.