Ohmic contacts to p-GaN were obtained after annealing Ni/Au and Ni/Au/Ni contacts in flowing O-2. Both Ni-capped p-GaN/Ni/Au and uncapped Ni/Au contacts were shown to result in specific contact resistance of similar to10(-4) Omega cm(2). In both cases, transparent NiO and thin, porous Au films were formed. Ni/Au contacts exhibited. optical transmittance at lambda = 450 nm of >85%. Addition of the Ni cap layer was shown to increase the thermal stability of thin Ni/Au ohmic contacts and increase the 450 nm transmittance to 93%, while maintaining a low contact resistance. The ability of the capping layer to produce these improvements was discussed based on a total energy model of thin film morphology.