We report on a metallization scheme of high reflectance, low resistance, and smooth surface morphology ohmic contact on p-type GaN. Ag–Cu alloy/Ru contact showed low contact resistivity as low as $6.2\times {10}^{-6}\Omega {\mathrm{cm}}^2$ and high reflectance of 91% at $460\mathrm{nm}$ after annealing at $400°\mathrm{C}$ in air ambient. The oxidation annealing promoted the out-diffusion of Ga atoms to dissolve in an Ag–Cu layer with the formation of an Ag–Ga solid solution, lowering the contact resistivity. The Ru overlayer acts as a diffusion barrier for excessive oxygen incorporation during oxidation annealing, resulting in high reflectance, good thermal stability, and smooth surface quality of the contact.