SiC device configurations comprising various polytypes have been analyzed using synchrotron white beam x-ray topography with the aid of computer simulation. Diffracted intensity maps for the various polytypes and their combinations in various diffraction geometries, including transmission, reflection, grazing-reflection and back-reflection are generated. This method is used to determine the structures of SiC devices fabricated via CVD epilayer growth of nominally 3C-SiC or 6H-SiC, or 6H-SiC substrates grown by the Lely technique. The work indicates that those devices which were initially considered to be of 3C structure also contain some 6H structure. Defect structures associated with the polytype configurations are also presented.