The behavior of amorphous Si in contact with Ag films and Ge in contact with Al films has been studied at temperatures well below those at which any liquid phase is present. MeV4He+ion backscattering techniques, transmission electron diffraction, scanning electron microscopy, and electron microprobe analysis have been used. We find that of the many possible reactions which carry the amorphous Si or Ge into their crystalline forms the reaction predominating under our experimental conditions consists of dissolution, diffusion, and crystal growth. During isothermal heat treatment, the semiconductor film is dissolved into the metal film where it diffuses and precipitates as crystalline Si or Ge. These processes are solid‐solid reactions, since this behavior is observed over temperatures of 300°C to as low as 100°C for Ge/Al, compared to the 424°C eutectic in this system. In Si/Ag, this behavior was observed from 700 to 400°C, compared with the 840°C eutectic.