PURPOSE: To prevent defective airtightness with the generation of cracks by fixing a cylindrical metal to a radiating electrode and using an annular flange for mutually fastening insulating members.

CONSTITUTION: A cylindrical metal 3 fast stuck to the side surface of a semiconductor substrate 1 is fixed to a radiating electrode 2, thus forming a base assembly B. A top assembly A is shaped by a compression bonded electrode 4 arranged adjacent to the substrate 1, a spring member 7 constituted of a washer 5 and springs 6, an insulating section 9 placed on an annular stepped section 8 formed to the electrode 4, an insulating member 10 and an annular flange 11. The annular stepped section is shaped to the electrode 4, and a columnar section 12 is formed at the central section of the electrode 4. Accordingly, defective airtight-ness with the generation of cracks is prevented.