We have investigated the effect of interfacial reactions between a Pt(7 nm)/Pd(7 nm)/Au(15 nm) layer and p-GaN on its ohmic contact properties by using Auger electron spectroscopy (AES), x-ray photoelectron spectroscopy (XPS), and glancing angle x-ray diffraction. The annealed Pt/Pd/Au contact exhibits linear current-voltage characteristics, which indicates that a high-quality ohmic contact is formed. The Pt/Pd/Au contact shows a specific contact resistivity of 3.1 x 10(-5) Omega cm(2) when annealed at 600degreesC for 2 min in flowing N-2 atmosphere. Both AES and XPS results show that the diffusion of Pt and Pd into the GaN surface region results in the formation of gallide and plays an important role in forming a low resistance ohmic contact by the creation of a highly doped p(+)-GaN surface region. (C) 2004 American Vacuum Society.