Disclosed herein is a nitride based semiconductor device, including: a substrate; a nitride based semiconductor layer having a lower nitride based semiconductor layer and an upper nitride based semiconductor layer on the substrate; an isolation area including an interface between the lower nitride based semiconductor layer and the upper nitride based semiconductor layer; and drain electrodes, source electrode, and gate electrodes formed on the upper nitride based semiconductor layer. According to preferred embodiments of the present invention, in the nitride based semiconductor device, by using the isolation area including the interface between the lower nitride based semiconductor layer and the upper nitride based semiconductor layer, problems of parasitic capacitance and leakage current are solved, and as a result, a switching speed can be improved through a gate pad.