Changes in film morphology upon annealing Ni and Ni/Au contacts to GaN were examined using scanning electron microscopy and atomic force microscopy. Atomic force microscopy was performed on the GaN surface that was exposed by etching away the metal film. This technique was demonstrated to be a convenient and effective way to evaluate the morphology of the contact/semiconductor interface, rapidly providing spatial information in three dimensions. Metal island formation and a corresponding deep, nonuniform metal penetration into GaN were observed after annealing Ni/GaN and Au/Ni/GaN contacts above 800 and 700 degrees C, respectively.