The measurement of thermally grown silicon dioxide films on selected metal silicides (CoSi2, CrSi2, Ir3Si5, NiSi2, Ru2Si3, and WSi2) via ellipsometry has been investigated. The oxide‐thickness calculation requires a knowledge of the complex refractive index of the metal‐silicide substrate which can be measured independently by ellipsometry on bare silicide substrates. In order to check the measured refractive indices for the silicide substrates, the thicknesses of thermally grown SiO2films were compared from ellipsometry which used the measured refractive indices, Rutherford backscattering, and step‐height thickness measurements. It is shown that, despite considerable complexities introduced by various surface treatments, procedures have been found so that effective refractive indices for the silicide substrates can be obtained, which in some instances require removal of the oxide and measurement of the complex refractive index of the silicide after oxidation.