In this paper, the interface vibrational spectrum in a reactive-sputtering a-Si:H/a-Ge:H muitilayer was investigated using IR transmission and Raman scattering. It is shown that excess deformation is not found near the interface and there is no evidence for excess hydrogen at the a-Si:H/a-Ge:H interface. The thermal stability of a-Si:H/a-Ge:H multilayer films was also studied by using IR and X-ray diffraction spectra. It was found that the crystallization temperature of a multilayer with small layer thickness is higher than that of bulk a-Ge:H.