Medium energy ion scattering, Fourier transform infrared spectroscopy and spectroscopic ellipsometry measurements have been performed on thermally grown SiO₂ layers on 4H silicon carbide. The data suggest the presence of a layer at the oxide–SiC interface consisting of both disordered Si and C. The infrared data indicate that the oxide layer is denser than fused silica. The thickness of the oxide layers as measured by spectroscopic ellipsometry agrees well with the values obtained from ion scattering.