Variable angle spectroscopic ellipsometry (VASE) has been used to characterize several SixGel-x/Ge heterostructures. First, SixGel-x/ Ge superlattice (SL) structures were characterized in terms of the layer thicknesses, composition, x, of the SixGel-x layer, and oxide thickness. High-resolution X-ray diffraction results are also presented for the SixGex-l/Ge SL structures and are shown to be in close agreement with the VASE results once strain effects are taken into account. VASE has also been used to study thick, Ge-rich SixGel-x/Ge heterostructures that have been grown on Si substrates. A stepped buffer has been deposited first in order to minimize the strain in the SixGel-x/Ge layers, VASE can be used to give a qualitative determination of the residual strain along with the thickness of all layers within the optical penetration depth from the surface.