Present disclosure provides a method for manufacturing a semiconductor device, including providing a substrate, forming a first III-V compound layer over the substrate, forming a first passivation layer over the first III-V compound layer, forming a first opening from a top surface of the first passivation layer to the first III-V compound layer, each opening having a stair-shaped sidewall at the first passivation layer, depositing a metal layer over the first passivation layer and in the first opening, the metal layer having a second opening above the corresponding first opening, and removing a portion of the metal layer to form a source electrode and a drain electrode.