We investigate Ni-Mg solid solution (4 nm)/ Pt (6 nm) metallization schemes for use in forming high-quality ohmic contacts to p-GaN: Mg (5 x 10(17) cm(-3)). The as-deposited Ni-Mg solid solution/Pt contact reveals nonlinear current-voltage characteristics. Annealing the contacts at 450 and 550 degreesC for 1 min in air ambient, however, improves electrical behaviors significantly. For example, specific contact resistance as low as 6.7 x 10(-5) Omega cm(2) is obtained, when the contacts are annealed at 450 degreesC. Based on the I-V measurement, Auger electron spectroscopy, and X-ray photoemission spectroscopy results, possible ohmic formation mechanisms for the Ni-Mg solid solution/Pt contacts are discussed. (C) 2004 The Electrochemical Society.