In order to reduce the driving voltage of DC electroluminescent (EL) devices, an electron injection structure with a hydrogenated amorphous Si (a-Si:H) interlayer between a Ta2O5 layer and ZnS:Mn layer was investigated. It was shown that junction capacitance existed between the Ta2O5 layer and ZnS:Mn layer and that the junction capacitance decreased due to the insertion of the a-Si:H layer. These results were confirmed by impedance spectra. The threshold voltage decreased with the insertion of the a-Si:H layer, and luminance gradually increased over the threshold voltage compared with that in conventional DC-EL devices, because the interlayer formed a stepwise band structure in the device. Moreover, the carrier multiplication effect of a-Si was confirmed under photoexcitation. Although a clear multiplication effect was not obtained, the possibility of further efficiency improvement by the multiplication effect was shown.