Three different conduction states, with typical impedances of 1010 Ω, 50 kΩ and 3 kΩ, have been found in hetero-junctions prepared by evaporation of the II-VI compound. A switching phenomena, with memory, is found to occur between two of the conduction states. The switching sequence is rapid (< 30 ns), and is found in junctions prepared from epitaxial and polycrystalline zinc selenide. The effect has also been observed in the p Si-n ZnS heterojunction system.