PURPOSE: To eliminate an inter-layer separation between insulating layers, to improve the heat conduction, and to maintain the insulating property in a good condition, by pressure-firing insulating layers of ceramic plates impregnated with an inorganic polymer at 400 to 600° C on a metal substrate, and holding and connecting a heating body between the layers.

CONSTITUTION: The first insulating layer 2 consisting of a ceramic paper is impregnated with an inorganic polymer and formed in a flat plate. The second insulating layer 4 consists of a ceramic paper being formed in a flat plate and also impregnated with an inorganic polymer. The first insulating layer 2 is placed on a metal substrate 1, and after a heating body 3 is arranged on the insulating layer 2, the second insulating layer 4 is placed to cover the heating body 3. And then a semicure treatment is applied at a temperature 250 to 350° C level. After the semicure, a pressure-firing is carried out at 400 to 600°C which is the hardening temperature of the inorganic polymer, and the connection is completed almost perfectly, and no inter-layer separation occurs between the insulating layers 2 and 4.