In an IC card, even when undershoot or overshoot which occurs upon an amplitude change by communication data is large, the change is accurately detected. A semiconductor device has antenna terminals, a power supply circuit for generating power supply voltage from an AC signal supplied to the antenna terminals, and a receiver circuit for demodulating an information signal superimposed on the AC signal. The receiver circuit includes a rectifier circuit, a filter circuit, a capacitor, an amplifier, a feedback path, a switch circuit, a binarizing circuit, and a control circuit. An output of the amplifier is transmitted to an inverting input terminal thereof, and the switch circuit is controlled by an output of the control circuit. In a predetermined period since level changes of an output of the binarizing circuit, the switch circuit is controlled to an off state by the output of the control circuit.