Semiconductor device

1. A semiconductor device, comprising:

a plurality of power amplifier circuits configured in a multistage-connected form,

wherein a first to a final stage of the plurality of amplifier circuits are formed over one semiconductor substrate of silicon,

wherein the plurality of amplifier circuits comprise field effect transistors,

wherein drain and source electrodes of the field effect transistors are respectively formed over a main surface and a back surface of the semiconductor substrate,

wherein the respective source electrodes of the plurality of field effect transistors are electrically connected to one another at the back surface of the semiconductor substrate,

wherein the respective source electrodes are connected to a fixed potential, and

wherein resistivity of the semiconductor substrate constituted of the silicon is in a range of about 1 mΩ·cm to about 10 mΩ·cm.

2. A semiconductor device according to claim 1 , wherein the power amplifier circuits operate in one bandwidth of an 800 MHz band, a 900 MHz band, an 1800 MHz band and a 1900 MHz band.

3. A semiconductor device according to claim 1 , wherein the semiconductor substrate is mounted over a wiring board, and the sources of the field effect transistors are respectively electrically connected to a fixed potential of the wiring board.

4. A semiconductor device according to claim 1 , wherein the semiconductor substrate is provided with passive elements for matching circuits.

5. A semiconductor device according to claim 4 , wherein the semiconductor substrate is mounted over a wiring board and provided with input and output matching circuits for each of the amplifier circuits.

6. A semiconductor device according to claim 4 , wherein shield layers are provided around the passive elements for the matching circuits, and wherein the shield layers are electrically connected to the semiconductor substrate through semiconductor regions and electrically connected to a fixed potential via an electrode over the back surface of the semiconductor substrate.

7. A semiconductor device according to claim 1 , wherein the semiconductor substrate is provided with a bias circuit and a control circuit used for the amplifier circuits.

8. A semiconductor device according to claim 1 , wherein a multiband system capable of coping with high frequency signals lying in a plurality of frequency bands is adopted for the semiconductor device.

9. A semiconductor device according to claim 1 , wherein the amplifier circuits respectively comprise three amplifying stages.

10. A semiconductor device, comprising:

first and second power amplifier circuits differing in operating frequency, which respectively comprise a plurality of amplifier circuits configured in a multistage-connected form; and

passive elements for matching circuits employed in the first and second power amplifier circuits and a bias circuit and a control circuit,

wherein a first to a final stage of the plurality of amplifier circuits of the first and second power amplifier circuits are formed over one silicon semiconductor substrate,

wherein the plurality of amplifier circuits respectively comprise field effect transistors,

wherein drain and source electrodes of the field effect transistors are respectively formed over a main surface and a back surface of the semiconductor substrate,

wherein the respective source electrodes of the plurality of field effect transistors are electrically connected to one another in the back surface of the semiconductor substrate,

wherein the source electrodes are respectively connected to a fixed potential, and

wherein resistivity of the semiconductor substrate is in a range of about 1 mΩ·cm to about 10 mΩ·cm.