PURPOSE: To obtain a snap operating disc member for a thermostat having a high operating temperature by providing a hardenable stainless steel and a high carbon alloy which have comparatively low (high) thermal expansion coefficient, similar elastic coefficient and can form a dish-like shape and can be hardened.

CONSTITUTION: A high temperature thermostat disc member 10 has a first layer of metal having a comparatively high thermal expansion coefficient metallurgically coupled to a second layer 14 of metal having a comparatively low thermal expansion coefficient. Both layers 12, 14 have similar expansion coefficient. In order to provide a disc which responds to a high temperature above 150°C, the first layer 12 includes an alloy B having expansion coefficient about 179-186×109Pa, a high carbon allay B or a high carbon alloy such as an alloy C. The second layer 14 includes a hardenable stainless steel having expansion coefficient about 179-200×109Pa. The second layer is put in the annealing state suitable to be formed into a dish-like shape, and heat treatment is made to increase the strength of the second layer 14 up to a level higher than the strength of the first layer 12.