We report on a study of Al and Ti/Al contacts ton-type GaN. Al contacts onn-GaN(7×1017 cm−3)annealed in forming gas at 600 °C reached a minimum contact resistivity of8×10−6 &OHgr; cm2and had much better thermal stability than reported by previous researchers. Ti/Al (35/115 nm) contacts onn-GaN(5×1017 cm−3)had resistivities of7×10−6and5×10−6 &OHgr; cm2after annealing in Ar at 400 °C for 5 min and 600 °C for 15 s, respectively. Depth profiles of Ti/Al contacts annealed at 400 °C showed that low contact resistance was only achieved after Al diffused to the GaN interface. We propose that the mechanism for Ohmic contact formation in Ti/Al contacts annealed in the 400–600 °C range includes Ti reducing the GaN native oxide and an Al–Ti intermetallic coming into intimate contact with the GaN. ©1997 American Institute of Physics.