To enable assembling of a small-sized semiconductor device of high performance at a low cost, by imparting heat dissipation capability to the surface of flexible composite, when a semiconductor chip is directly mounted on a circuit board.

Flexible composite 4 is fixed between a substrate electrode 5 of a circuit board 2 and a semiconductor chip electrode 3. The flexible composite 4 is formed by coating the surface of elastomer, elastomer powder filler, rubber, etc., with ceramics, and a heat dissipating layer 6 is formed. The flexible composite 4 fixes a semiconductor chip 1 to the circuit board 2, and dissipates heat generated by a semiconductor device during operation. The flexible composite 4 has flexibility and so can sufficiently exhibit thermal stress when the semiconductor is mounted. Thereby a small-sized semiconductor device of high performance can be easily assembled at a low cost.