A power supply semiconductor IC includes: an output transistor connected between a voltage-input terminal and a voltage-output terminal; a control circuit that controls the output transistor based on a feedback voltage of an output voltage; a current-limit circuit that limits an output current of the output transistor such that the output current is not equal to or greater than a current limit; a first transistor constituting a current-mirror circuit with the output transistor; a short-circuit-fault detection circuit that detects a short circuit of the voltage-output terminal based on a voltage across a resistor connected in series to the first transistor; and a first output terminal that outputs a detection result of the short-circuit-fault detection circuit. The current limit is within a detection range of the short-circuit-fault detection circuit. The short-circuit-fault detection circuit detects a short circuit of the voltage-output terminal even while the current limit circuit limits the output current.