We report on the thermal stability of Pt and Pd thin films on GaN up to 800 °C. We have found that for Pt thin films submicron size metal spheres form at temperatures as low as 600 °C and the film turns into discontinuous islands at 725 °C and above. Pd begins to form islands above 700 °C and areas of the film begin to delaminate due to thermally generated compressive stress. The general behavior of these films is that found for most metal films on ceramics, suggesting that metals on GaN do not react as they typically do on common elemental and compound semiconductors. This ceramic-like behavior must be considered when determining which metals may act as good electrical contacts for GaN, especially for high temperature applications or alloyed contacts. ©1997 American Institute of Physics.