PURPOSE: To make a high-density wiring circuit board being excellent in heat radiation and having a thermal expansion coefficient equivalent to an LSI chip mounted on a substrate, so as to prevent the thermal breakdown at a temperature rise, by making it of plate-shaped granular silicon sintered body.

CONSTITUTION: An insulating cover layer 2 is made on a substrate 1 consisting of a plate-shaped granular polysilicon sintered body. A plurality of LSI bare chips 3 are joined on the insulating cover layer 2 through solder material 4. Furthermore, circuit wiring 5 consisting of a metallic film is made at the insulating cover layer 2, and the LSI bare chip 3 and the circuit wiring 5 are electrically connected with each other by a bonding wire 6. Here, the plate-shaped granular silicon sintered body has a high heat conductivity equal to an aluminum nitride, and is not only excellent in heat radiation, but also does not cause thermal breakage at temperature rise because it the thermal expansion coefficient is equal to the LSI chip mounted on the substrate. Moreover, it is fitted to ultrahigh-speed drive because the permittivity of board is lower than a ceramic board such as an aluminum nitride, and the wiring capacity can be lowered.