Abstract 3C–SiC thin films have been investigated by means of high resolution X-ray diffraction techniques ( ω/2Θ-scan, ω-scan) and X-ray topography. The SiC films were grown in a solid source molecular beam epitaxy (MBE) system on 6H–SiC substrate crystals. We investigate the lattice mismatch parallel and perpendicular to the -direction using the so-called reciprocal space mapping technique. When 3C–SiC films were grown on 6H–SiC substrates, double position boundaries (stacking sequence ACB instead of ABC) were frequently observed. For the visualization of this effect high resolution X-ray topographic measurements are investigated at 3C–SiC layers on 6H–SiC substrates. We find, that the domains of different stacking sequences are equally distributed in the 3C–SiC epilayer. This domains attain a size up to approximately 200×200 μm 2.