A low-resistance ohmic contact to Mg-doped p-type GaN grown by metal-organic chemical vapor deposition (MOCVD) with a carrier concentration of 2 x 10(17) cm(-3) using Pd/Ni/Au metallization was formed. An anneal at 500 degrees C for 1 min in a flowing N-2 ambient produced an excellent ohmic contact with a specific contact resistivity as low as 2.4 x 10(-5) K-2 Cm-2. X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) depth profiles of Pd/Ni/Au contacts annealed at 500 degrees C demonstrated a strong correlation between Ni and Pd interdiffusion toward the GaN surface and a reduction in specific contact resistance. The low contact resistance is attributed to the reduction of the native oxide by Ni diffusion along with the formation of Pd and Ni related-gallide phases at the p-GaN surface region. (c) 2005 Elsevier Ltd. All rights reserved.