Abstract: A method for preparing single-crystal ZnSe comprising the steps of:working polycrystalline ZnSe into a rod-shaped starting material;placing the starting material in a reaction vessel;filling the atmosphere of the reaction vessel with an inert gas, nitrogen, H.sub.2 Se gas, or a mixture thereof at from about 0.1 to about 100 Torr; andconverting the polycrystalline ZnSe starting material to single-crystal ZnSe, while maintaining a solid phase, by moving the reaction vessel at a rate of from about 0.05 to about 5 mm/day through a temperature profile consisting of a cool zone AB having a temperature T.sub.1 in the range of from about room temperature to about 100.degree. C., a temperature increasing zone BC having a temperature gradient of from about 50.degree. to about 200.degree. C./cm, a hot zone CD having a temperature T.sub.2 in the range of from about 700.degree. to about 900.degree. C., a temperature decreasing zone DE having a temperature gradient of from about -200.degree. to about -50.degree. C.