The morphological instability of copper germanide (Cu3Ge) films in contact with amorphous germanium is reported. Through secondary ion mass spectrometry, x‐ray diffraction, transmission electron microscopy, and electrical measurements, the breakdown of the continuous layer has been monitored. On the contrary, with Cu3Ge in contact with single crystal germanium, no instability is observed at the same temperature. The crystallization of the amorphous germanium appears to be the mechanism responsible for the instability. ©1995 American Institute of Physics.