A semiconductor device includes a first nonlinear element, an differential amplifier that generates a differential signal from a signal output by the first nonlinear element; a first and second insulating elements that are connected to a non-inverting signal output terminal and an inverting signal output terminal of the differential amplifier, respectively; first to third nonlinear elements each outputting a first logic level if the received signal is equal to or larger than a given threshold value, and outputting a second logic level if the received signal is smaller than the given threshold value; and a logic circuit that outputs the logic level output by the second nonlinear element if the logic levels output by the second and third nonlinear elements are different from each other, and makes the logic level of the output signal unchangeable when the second and third nonlinear elements output the same logic level.