A method of manufacturing a nitride semiconductor device including: forming a nitride semiconductor layer over a substrate wherein the nitride semiconductor layer has a 2DEG channel inside; forming a drain electrode in ohmic contact with the nitride semiconductor layer and a source electrode spaced apart from the drain electrode, in Schottky contact with the nitride semiconductor layer, wherein the source electrode has an ohmic pattern in ohmic contact with the nitride semiconductor layer inside; forming a dielectric layer on the nitride semiconductor layer between the drain electrode and the source electrode and on at least a portion of the source electrode; and forming a gate electrode on the dielectric layer to be spaced apart from the drain electrode, wherein a portion of the gate electrode is formed on the dielectric layer over a drain-side edge portion of the source electrode.