Semiconductor device

1. A semiconductor device comprising:

a first well provided in a semiconductor substrate;

a second well provided in the semiconductor substrate, so as to be isolated from the first well;

a Schottky barrier diode provided in the first well;

a transistor formed in the second well;

a first signal line connected to one terminal of the Schottky barrier diode, and through which a source voltage or a reference voltage is applied; and

a second signal line connected to the other terminal of the Schottky barrier diode and the second well, through which a voltage different from the source voltage and from the reference voltage is applied.

2. The semiconductor device of claim 1 , further comprising;

a third well provided in the semiconductor substrate, so as to be isolated from the first well and the second well; and

a PN junction diode formed in the third well, with an impurity concentration of the PN junction thereof set higher than an impurity concentration of the Schottky junction of the Schottky barrier diode, and being connected antiparallel with the Schottky barrier diode.

3. The semiconductor device of claim 1 ,

wherein the semiconductor substrate has in the surficial portion thereof an epitaxially-grown semiconductor layer, and

the second well is located deeper than the epitaxially-grown semiconductor layer.

4. The semiconductor device of claim 1 ,

wherein the semiconductor substrate has in the surficial portion thereof an epitaxially-grown semiconductor layer, and

the first well extends from the surface of the epitaxially-grown semiconductor layer.