Provided is a semiconductor device including a target circuit, a monitoring circuit, and a voltage controller. The target circuit includes a transistor. The monitoring circuit is configured to measure a temperature of the target circuit or measure a delay time between an input and an output of the target circuit. The voltage controller is configured to adjust a driving voltage for driving the target circuit or a back-bias voltage for adjusting a threshold voltage of the transistor by referring to at least one of the temperature and the delay time. As the temperature increases, the delay time decreases.