We report on a promising metallization scheme for high-quality Ohmic contacts to surface-treated p-GaN:Mg (2–3×1017 cm-3). It is shown that the as-deposited Pt/Ru contact produces a specific contact resistance of 7.8(±2.2)×10-4 Ω cm2. However, annealing of the contact at 600 °C for 2 min results in a resistance of 2.2(±2.0)×10-6 Ω cm2. It is also shown that the light transmittance of the annealed contact is 87.3% at 470 nm. Furthermore, the surface of the contact annealed at 600 °C for 30 min is found to be very smooth with a rms roughness of 0.8 nm. These results strongly indicate that the Pt/Ru can be a suitable scheme for the fabrication of high-performance laser diodes or other devices. © 2000 American Institute of Physics.