A semi-kinematic approach to x-ray diffraction of real crystals with small defects is proposed by incorporating an extinction function into the kinematic diffraction formula. The effect of multiple reflections is described by the extinction coefficient which can be calculated by Darwin’s recursion relations. In this approach the intensity of the coherent scattering is related to the static Debye–Waller factor E, while the intensity of diffuse scattering is determined by the correlation function of the distortion field. When E=1, i.e., for perfect crystals, it gives exactly the same result as Darwin’s theory does. The feasibility of this approach is demonstrated by investigating the reciprocal space mapping and the crystal truncation rod of a GaAs crystal. ©1997 American Institute of Physics.