Patent ID: 6858918

Claim:
A semiconductor device comprising: a fixed capacitance formed in a semiconductor substrate and having a capacitance value fixed; and a variable capacitance formed in said semiconductor substrate and capable of variably controlling a capacitance value, wherein said fixed and said variable capacitance, are connected to each other in parallel, wherein said variable capacitance includes a junction capacitance formed by a PN junction portion, said semiconductor substrate includes a semiconductor substrate of a first conductivity type, and said junction capacitance includes; a first semiconductor region of a second conductivity type provided in an upper layer portion of said semiconductor substrate, said first semiconductor region having a PN junction portion together with a region of the first conductivity type of said semiconductor substrate; a second semiconductor region of the first conductivity type provided in said upper layer portion of said semiconductor substrate; and an isolating region provided in said upper layer portion of said semiconductor substrate and serving to isolate said first and second semiconductor regions.