A high voltage durability III-nitride semiconductor device comprises a support substrate including a first silicon body, an insulator body over the first silicon body, and a second silicon body over the insulator body. The high voltage durability III-nitride semiconductor device further comprises a III-nitride semiconductor body characterized by a majority charge carrier conductivity type, formed over the second silicon body. The second silicon body has a conductivity type opposite the majority charge carrier conductivity type. In one embodiment, the high voltage durability III-nitride semiconductor device is a high electron mobility transistor (HEMT) comprising a support substrate including a silicon layer, an insulator layer over the silicon layer, and a P type conductivity silicon layer over the insulator layer. The high voltage durability HEMT also comprises a III-nitride semiconductor body formed over the P type conductivity silicon layer, the III-nitride semiconductor body forming a heterojunction of the HEMT.