A semiconductor device capable of adjusting profiles of a gate electrode and a gate spacer by implanting or doping an element semiconductor material into an interlayer insulating layer may be provided. The semiconductor device may include a gate spacer on a substrate, the gate spacer defining a trench, a gate electrode filling the trench, and an interlayer insulating layer on the substrate, which surrounds the gate spacer, and at least a portion of which includes germanium.