Some new experimental data concerning the characterization of ZnS : Mn thin-film electroluminescent devices with the inherent memory, which is due to a hysteresis of the voltage dependence of the luminance and transferred charge, are reported. Essential differences in the kind, number and energy depth of defects depending upon the magnitude of the hysteresis effect have been revealed by the study of the photodepolarization spectra. An estimation of a contribution of the impact ionization of the lattice and defects to the generation of a positive space charge responsible for the hysteresis has been carried out. Peculiarities in the temperature and frequency dependencies of the hysteresis width, threshold voltage and extinction voltage have been found in the devices, showing the different memory margin. The role of different defects in the memory effect is discussed with the allowance for the obtained results and published data.