PURPOSE: To provide high heat conductivity, to fix a conductor pin rigidly at a short interval and to enhance reliability in electrical connection, by providing the diameters of the flange part of the conductor pin in the vicinity of a supporting part so that one diameter is larger than the internal diameter of a through hole and the other diameter is smaller than said internal diameter.

CONSTITUTION: A semiconductor mounting substrate is provided with the following parts: a metal substrate 1 having a through hole 2, an insulating layer 3, which is formed by burying an insulating material in the through hole, a through hole 4, which is formed at the approximately central part of the insulating layer 3 and has a cross sectional corner part of about 90°, and a conductor pin 6, which is fixed to the through hole 4 with a supporting part 7. The diameters of a flange part 8 of the conductor pin 6 in the vicinity of the supporting part 7 are set so that one diameter is larger than the internal diameter of the through hole 4 and the other diameter is smaller than said internal diameter. The conductor pin 6 is fixed to the through hole 4 with a solder 9. Thus, the conductor pin 6 is rigidly fixed to the through hole 4 without loosing high heat conductivity of the semiconductor mounting substrate, in which metal is used as a core. Reliability in electrical connection is also enhanced.