A comparison was made of the forward current-voltage characteristics of bulk GaN Schottky and p-n junction rectifiers using a quasi-three-dimensional simulator. The model includes incomplete ionization of the deep Mg acceptor (175 meV) in the p + -GaN side of the junction and the temperature dependence of mobility and GaN band gap. The forward turn-on voltages, V F , decrease with increasing temperature for both types of rectifier and are ~2.5 V at 100 Acm - 2 at 573 K for the junction diodes and =<1 V under similar conditions for the Schottky diodes. The effect of p-layer thickness and doping in the p-n junction was also investigated.