A semiconductor device with a built-in battery whose residual amount of the electrical energy can be detected accurately. The semiconductor device has a battery, a demodulation circuit, a control circuit which generates a signal having information about the residual amount of the electrical energy stored in the battery, and a transmission medium which displays the residual amount of the electrical energy in accordance with the signal. The demodulation circuit demodulates a signal input from an antenna which requests display of the residual amount of the electrical energy. Based on the demodulated signal, the control circuit starts to generate a signal having information about the residual amount of the electrical energy in the battery.