PURPOSE: To prevent from the deterioration of property of an analog circuit by separating a power source line of a digital circuit and an analog circuit in an analog/digital circuit mixed LSI, and supplying the lower source voltage than that of the analog circuit to the digital circuit, thereby decreasing the generation of noises in the digital circuit.

CONSTITUTION: A semiconductor chip 1 is composed of an analog circuit 2 and a digital circuit 3 in a mixture on it. A source voltage 4a and a source voltage terminal 4b are installed individually corresponding to the analog circuit 2 and the digital circuit 3, respectively. The source voltage VA ranging from +5V to +10V is impressed on the source voltage terminal 4a for the said analog circuit. On the other hand, the source voltage VD ranging from +1V to +5V which is lower than that of the said source voltage VA is impressed on the source voltage terminal 4b for the digital circuit. Therefore, it is possible to decrease the voltage of switching amplitude of a transistor of the digital circuit, and to reduce the switching noises to be generated in a semiconductor substrate or a power source line.