A semiconductor device capable of achieving desirable communication behavior through a bus regardless of whether or not a pull-up resistor is connected on a bus line. The semiconductor device includes external pull-up determination unit and internal pull-up setting unit. The external pull-up determination unit applies a pull-down voltage through an internal pull-down resistor to the bus line, and determines whether an external pull-up resistor external to the semiconductor device is connected on the bus line on the basis of the voltage level of the bus line when the pull-down voltage is applied to the bus line. The internal pull-up setting unit stops application of the pull-down voltage, and applies a pull-up voltage through an internal pull-up resistor to the bus line if it is determined that no external pull-up resistor is connected on the bus line. The internal pull-up setting unit stops application of the pull-down voltage if it is determined that the external pull-up resistor is connected on the bus line.