The advent of new semiconductor materials frequently demands new methods of investigating and defining those growth flaws which can degrade device performance. A new x‐ray topographic method and concept were developed to study the defect structures in the heteroepitaxial systems. Compositional x‐ray topography is an extension of the scanning‐reflection method, which permits a nondestructive evaluation of the perfection in the substrate, deposit, and heterojunction. The theory and limitations of this method are discussed. Compositional x‐ray topography was applied to the study of homogeneity and perfection in various heteroepitaxial systems, i.e. , , .