A semiconductor device including a group III-V barrier and a method of manufacturing the semiconductor device, the semiconductor device including: a substrate, insulation layers formed to be spaced apart on the substrate, a group III-V material layer for filling the space between the insulation layers and having a portion protruding higher than the insulation layers, a barrier layer for covering the side and upper surfaces of the protruding portion of the group III-V material layer and having a bandgap larger than that of the group III-V material layer, a gate insulation film for covering the surface of the barrier layer, a gate electrode formed on the gate insulation film, and source and drain electrodes formed apart from the gate electrode. The overall composition of the group III-V material layer is uniform. The barrier layer may include a group III-V material for forming a quantum well.