A method of manufacturing a nitride semiconductor device is disclosed. The method includes forming a gallium nitride (GaN) epitaxial layer on a first support substrate, forming a second support substrate on the GaN epitaxial layer, forming a passivation layer on a surface of the other region except for the first support substrate, etching the first support substrate by using the passivation layer as a mask, and removing the passivation layer and thereby exposing the second support substrate and the GaN epitaxial layer.