The specific features of defects of crystal lattices in multilayer device structures containing small-period (T ≲ 20nm) superlattices of type-I ZnSe/ CdxZn1−xSe/ZnSe/.../ZnSe/(001)GaAs and type-II ZnS/ZnSe1−xSx /ZnS/.../ZnS/(001)GaAs were studied by the methods of X-ray diffractometry and diffraction rocking pseudocurves, and partially by the X-ray topography. According to the data of quantitative analysis of the X-ray diffraction spectra, the periods of superlattices ranged from TI = 11.3 to 16.1nm (for the compositions CdxZn1-xSe with x1 = 0.047 and x2 = 0.107) for type-I superlattices and TII = 15.6 to 17.2nm for type-II superlattices (for the compositions ZnSe1-xSx with x1 = 0.20 and x2 = 0.10). The widths of diffraction peaks from both the ZnSe layers and small-period superlattices in the diffraction rocking pseudocurves considerably exceed their widths in the X-ray diffraction spectra. This fact proved that a pronounced plastic strain with the formation of series of rectilinear dislocations in the crossing slip systems took place in the studied device structures. In order to exclude the generation of dislocations in the growth processes, it was necessary to decrease the concentration of the solid solution to the values x < 0.047 for the first type of superlattices and to the values x ≲ 0.062 for the second type of superlattices, and to decrease the thickness of the ZnSe and ZnS layers.Defects of the Structure of Semiconductor Superlattices Grown on the Basis of II–VI Alloys. G.F.Kuznetsov: Semiconductors, 2007, 41[10], 1255-62