To uniformly heat-treat whole area of wafer surface and lower the electric resistance by carrying out heat treatment under specific conditions in a method for heat-treating ZnSe wafer in zinc melt.

ZnSe wafer is heat-treated in stationary convection current of zinc melt which flows to the upper direction or lower direction. ZnSe wafer is supported by left and right end parts and the upper and lower end parts are released and whole area of wafer is retained in stationary convection current of the zinc melt. The surrounding lower part of a heat-treating vessel is heated by arranging a heater in the surrounding lower part and the center part of the bottom of the vessel is retained to relatively low temperature by bringing into contact with a heat-releasing body and upward flow is given to the zinc melt in the circumference of the vessel and downward flow is given to the center of the vessel.