This invention provides a semiconductor device contrived to prevent a reference voltage and a reference current which are supplied to a high speed OCO from varying with a change in ambient temperature and/or a change in an external power supply voltage and to reduce the circuit area of a power supply module. The high speed OCO outputs a high speed clock whose magnitude is determined by the reference current and the reference voltage. A temperature sensor detects the ambient temperature of the high speed OCO and a voltage sensor detects the operating voltage of the high speed OCO. The power supply module includes a BGR and generates the reference voltage, reference current, and operating voltage of the high speed OCO, based on a primary reference voltage which is output by the BGR. A flash memory stores a table specifying trimming codes for the reference voltage and reference current, related to an ambient temperature and an operating voltage of the high speed OCO. A logic unit adjusts the values of the reference current and reference voltage, according to the reference voltage and reference current trimming codes related to the detected ambient temperature and operating voltage.