Undoped, 4µm thick GaN layers grown by Metal Organic Chemical Vapor Deposition were used for fabrication of high stand off voltage (356 V) Schottky diode rectifiers. The figure of merit VRB
2/RON, where VRB is the reverse breakdown voltage and RON is the on-resistance, was ~ 4.53 MW-cm−2 at 25°C. The reverse breakdown voltage displayed a negative temperature coefficient, due to an increase in carrier concentration with increasing temperature. Secondary Ion Mass Spectrometry measurements showed that Si and O were the most predominant electrically active impurities present in the GaN.