Parallel investigations of Raman scattering and spectroscopic ellipsometry of plasma-enhanced chemical vapor deposited SiO2 on InSb was carried out. The purpose was to obtain more comprehensive information about the structure and composition of the deposited layers. These consist of stoichiometric and homogeneous SiO2. An interface layer of a significant thickness of 130 Angstrom whose optical constants differ from those of the basic film is observed. The interlayer is composed of sublayers as a result of a chemical reaction of the InSb natural surface oxide and the plasma environment during deposition.