4H-SiC commercial wafers and sublimation grown epitaxial layers with a thickness of 100 mum have been studied concerning crystalline structure. The substrate wafers and the epitaxial layers have been separately investigated by high-resolution x-ray diffraction (HRXRD) and synchrotron white beam x-ray topography (SWBXT). The results show that the structural quality was improved in the epitaxial layers in the < 11 (2) over bar0 > and <(1) over bar 100 > directions, concerning domain distribution, lattice plane misorientation, mosaicity, and strain? compared with the substrates. Misoriented domains have merged together to form larger domains while the tilt between the domains was reduced, which resulted in non-splitting in diffraction curves. It is also clear that if the misorientation in the substrate gets too large, we can only see a slight decrease in the misorientation in the layer. At some positions on the substrates there were block structure (mosaicity). omega -rocking curves from epilayers at the same position showed smaller full width at half-maximum (FWHM) values and more uniform and narrow peaks. Curvature was almost the same in grown epilayers compared with the substrates. The shape of the grown epitaxial layers nas concave similarly to the substrates.