ZnSe-based organic-inorganic heterostructure diodes in which ZnSe layer was fabricated by electron-beam evaporation were studied. Electroluminescence from ZnSe peaking at 578nm was observed from bilayer device ITO/ZnSe(50nm)/Alq3(12nm)/Al, but it is difficult to observe any EL emission from single-layer diode ITO/ZnSe(50—120nm)/Al. Based on this, we further introduced a PVK or NPB hole-transporting layer (HTL), to make trilayer devices ITO/HTL/ZnSe/Alq3/Al to investigate the influence of ZnSe layer on the emission of the trilayer devices by varying the device structure. Our experimental data of EL emission confirm the roles played by ZnSe in these devices of transporting not only electrons but also holes, as well as acting as an emissive layer. Furthermore, a luminescence mechanism of charge carriers injection luminescence in ZnSe layer is suggested.