An amorphous Ge‐Au(a‐Ge‐Au) film prepared by vacuum deposition was studiedinsituand irradiated by an electron beam in a transmission electron microscope. The amorphous Ge‐Au film can be crystallized rapidly and locally by electron beam irradiation, forming polycrystalline metastable Ge0.4Au0.6tetragonal phase and then decomposing to polycrystalline Ge and polycrystalline Au at increased irradiation dose. The results suggest that the crystallization ofa‐GeAu film, the formation of Ge0.4Au0.6and the decomposition of the metastable Ge0.4Au0.6are dependent on the temperature rise of the irradiation process. ©1996 American Institute of Physics.