Artificial multilayers of amorphous Si and amorphous Si containing 0.7 at. % Au, with repeat lengths between 44 and 48A, were fabricated by ion beam sputtering. The change, with annealing time in the intensity of the first‐order x‐ray diffraction peak resulting from the composition modulation, is used to determine the diffusivity of Au in amorphous Si. Diffusion lengths on the order of an interatomic distance have been measured. The diffusivities over the temperature range 200–260 °C have an Arrhenius‐type temperature dependence with an activation enthalpy of about 1.3 eV, and are in agreement with the extrapolation of published higher temperature data.