The X-ray diffractometric Ω-Scan method needs only one measuring circle to determine the lattice geometry of single crystals. From the angular positions of at least two reflection pairs the orientation in a certain range can be precisely determined. For cubic crystals the lattice parameter related to a reference crystal can be calculated additionally. The method is applied to the adjustment of crystal ingots for the succeeding processing and to the characterization of wafers. By means of an x–y table the distribution of the structural parameters over the wafer surface can be mapped with a lateral resolution of about 1 mm. In a Si1−xGex sample, characteristic concentric distributions have been found with orientation changes up to 3 arc minutes and lattice-parameter differences up to 2.8 × 10−5 nm, corresponding to differences of the Ge content up to 1.4 at%.