The method of the invention for producing a group III-V semiconductor device includes forming, on a base, a plurality of semiconductor devices isolated from one another, each semiconductor device having at least an n-layer proximal to the base, and a p-layer distal to the base, and having a p-electrode formed on the top surface of the p-layer, and a first low-melting-point metal diffusion preventing layer, the low-melting-point metal diffusion preventing layer being formed on the top surface of the p-electrode; forming, from a dielectric material, a side-surface protective film so as to cover a side surface of each 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.