Abstract: A method of joining together a pair of members each having a high thermal conductivity includes forming a joining surface of a first of these two members with either of a plurality of projecting portions and a plurality of projecting and recessed portions; forming a joining surface of a second of the extruded members with either a plurality of recessed portions each of which corresponds to a selected one of the projecting portions and a plurality of projecting portions each of which corresponds to a selected one of the recessed portions of the projecting and recessed portions of the first member; and inserting under pressure each of the projecting portions of one of the two extruded members into each of the recessed portions that corresponds thereto, of another of the two extruded members, with a tolerance that is sufficient to induce a plastic deformation in each of the members.