High-frequency semiconductor device including a semiconductor chip

A semiconductor device includes a silicon substrate with a resistivity being raised by diffusing Au etc. therein, and includes both active elements and passive elements. The active elements are all placed within a semiconductor chip, and the semiconductor chip is flip-chip mounted over the silicon substrate. Such a case where the silicon substrate is heated due to a heating process for forming the active elements can be avoided, and therefore, diffusion of Au etc. from the silicon substrate into the semiconductor device can be avoided.