This paper reports on the n-type ZnS used as electron transport layer for the organic light-emitting diodes(OLEDs). The naphthyl-substituted benzidine derivative (NPB) and tris (8-hydroxyquinoline) aluminium (Alq3)are used as the hole transport layer and the emitting layer respectively. The insertion of the n-type ZnS layer enhances the electron injection in the OLEDs. The study was carried out on OLEDs of structures: indium-tin-oxide (ITO)/NPB/Alq3/ZnS/LiF/AL, ITO/NPB/Alqa/LiF/AL and ITO/NPB/Alq3/AL. The luminance and efficiency of the device containing this electron transport layer are increased significantly over those obtained from conventional devices due to better carrier balance.