A semiconductor device provided which includes: an external power supply detection circuit which detects that an external power supply is turned on and outputs a first detection signal; an internal power supply voltage generation circuit which generates an internal power supply voltage based on the external power supply; a reference voltage generation circuit which generates a first reference voltage in response to the first detection signal; a reference voltage detection circuit which detects that the first reference voltage reaches a given level and outputs a second detection signal; a bias voltage generation circuit which, in response to the second detection signal, generates a bias voltage based on a second reference voltage dependent on the first reference voltage; and a power supply voltage detection circuit which, in response to the second detection signal, compares the bias voltage with a third reference voltage and outputs a start signal.