A semiconductor device includes an integration of a first external terminal to which a DC input voltage is input, a second external terminal to which a rectifying and smoothing circuit is externally connected, an output transistor connected between the first external terminal and the second external terminal, a control circuit arranged to turn on and off the output transistor so that a desired DC output voltage can be obtained from the rectifying and smoothing circuit, a current detection circuit arranged to generate a sense voltage corresponding to an on-current of the output transistor, and an overcurrent protection circuit arranged to monitor the sense voltage so as to perform an overcurrent protection operation. The overcurrent protection circuit performs a first overcurrent protection operation of a pulse-by-pulse method when detecting that the sense voltage exceeds a first threshold value voltage, and performs a second overcurrent protection operation of a timer latch method when detecting that the sense voltage continues to increase though the first overcurrent protection operation is being performed.