A method for producing a Group III-V semiconductor device, includes forming, on a base, a plurality of semiconductor devices isolated from one another, forming, through ion implantation, a high-resistance region in a surface layer of a side surface of each semiconductor device, after formation of the high-resistance region, forming a p-electrode and a low-melting-point metal diffusion prevention layer on the top surface of the semiconductor device, bonding the semiconductor device to a conductive support substrate via a low-melting-point metal layer, and removing the base through the laser lift-off process.