We have studied growth mode and defect generation in heteroepitaxy of ZnSe on Te-terminated GaAs(001) surfaces. The high saturation coverage of Zn on Te-terminated GaAs enhances the layer-by-layer growth of ZnSe. However, high densities of faulted defects (similar to 5 x 10(8)/cm(2)) are generated in the ZnSe film. We have found that the generation of defects is not necessarily ascribed to an island growth mode, but is closely related to the formation of a vacancy-contained Ga-Te interface layer.