To attain high thermal conductivity in a GaN substrate for high voltage driving element.

After forming an element by forming a GaN element on a sapphire substrate, a glass substrate is stuck to the element surface via a UV peelable material. Subsequently, the sapphire substrate and a GaN layer are removed by laser irradiation. Thereafter, the back side of the GaN element thus removed is metallized and a heat sink substrate is stuck thereto. Under that state, the glass surface is irradiated with UV light, thus removing the glass substrate. Consequently, a GaN element is formed on a heat sink. Since the heat sink substrate has a two-layer structure of a conductive heat sink material, and an insulating material, the element potential and the lead frame potential can be isolated.