The crystal structure of ZnS single crystals grown from melt has been found to be cubic zinc blende by the x‐ray analysis of oscillation photographs. However, the x‐ray ⟨111⟩ axis oscillation patterns of the crystals synthesized by various methods are symmetric about the equator line and some spots are elongated alongc*, whereas the patterns of natural crystals are asymmetric and sharp. Therefore, it is concluded that the synthetic ZnS crystal contains a considerable amount of stacking disorder in the close‐packed planes due to growth faults which result in two orientations in the crystal structure (twin orientations) that repeat with a relatively short periodicity. The value of fault probability occurring in the (111) plane can be obtained by superimposing the observed diffuse diffraction spectra with the ones calculated numerically by a formula proposed by Paterson for the growth fault. This value is also compared with that obtained from the transmission electron micrographs.