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X‐ray topography images in the form of contrast rosettes from edge dislocations of the slip system in ZnGeP2 single crystals, obtained under different diffraction conditions, are identified and interpreted. To analyze and model the dislocation images, a semi‐phenomenological theory of contrast is applied. The simulation of images of edge dislocations under Borrmann effect conditions was carried out in cases when the diffraction vector was parallel or perpendicular to the slip plane of the dislocation. In both cases, the main part of the experimental image is formed because of waveguiding of Bloch waves in the regions of tension and compression of the lattice on either side of the slip plane. Additional image details arise through relaxation of stresses at the exit surface. Since the color of all lobes of the contrast rosette is related to the sign of the deformation, the location of the dislocation half‐plane is unambiguously determined. Thus, from the form of the rosette image, it is possible to obtain the slip plane, the magnitude and sign of the Burger's vector, and the direction of the dislocation line.

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The first study of structural defects in a ZnGeP2 semiconducting nonlinear optical crystal has been carried out by X‐ray topography, based on the Borrmann effect, and the effect of anomalous transmission of X‐rays on ZnGeP2 crystals has been examined. It is shown that the rosette technique of defect study under conditions of the Borrmann effect, developed earlier for elementary semiconductors, can be applied to the study and identification of defects in ZnGeP2. Features of contrast from individual edge and screw dislocations, microdefects, and coherent and semi‐coherent microinclusions were considered. Defect identification was carried out by comparison of the experimental intensity contrast with simulated images of the defects.