In this paper, we report the investigation of the thermal enhancement and the behavior of GaN Schottky diodes grown by metal organic chemical vapor deposition (MOCVD) on sapphire substrates for RF power applications and their potential to operate under extreme temperature. The Schottky barrier diodes show a Schottky barrier height (ϕB) close to 0.93 eV and an ideality factor (η) near unity with 1.03. Pt/Au anodes annealed at 500°C and 600ºC show an improvement of the electrical characteristics and a breakdown voltage as high as 130 V for a drift layer thickness of 1 µm and doping of 10^16 cm-3.