A semiconductor device includes a reference voltage generating section configured to generate a first reference voltage and a second reference voltage based on a voltage supplied from an external power supply, and an AD (analog/digital) conversion circuit operating based on the first reference voltage to generate an AD conversion signal corresponding to an output signal supplied from an external device. The second reference voltage is supplied to the external device, and a ratio of the first reference voltage and the second reference voltage is kept to a constant value regardless of a temperature of the semiconductor device.