The invention discloses a process of forming an ohmic electrode containing aluminum (Al) on a nitride semiconductor material. The process includes steps of: (a) depositing an ohmic metal on the semiconductor material; (b) forming an insulating film such that the insulating film covers a side of the ohmic metal but exposes a top of the ohmic metal; and (c) alloying the ohmic metal at a temperaturehigher than 500 degree centigrade for 30 to 60 seconds.