Disclosed herein is a nitride based semiconductor device. There is provided a nitride based semiconductor device including: a base substrate; an epitaxial growth layer disposed on the base substrate and generating 2-dimensional electron gas (2DEG) therein; and an electrode structure disposed on the epitaxial growth layer and having an extension extending into the epitaxial growth layer, wherein the epitaxial growth layer includes a depressing part depressed thereinto from the surface of the epitaxial growth layer, and the depressing part includes: a first area in which the extension is disposed; and a second area that is an area other than the first area.