A semiconductor device comprises a pulse signal output circuit providing a pulse signal for a transmission electrode of an electrode pair, a current converter converting a first current generated on the reception electrode to a second current, a current-controlled oscillator outputting an oscillation signal having a frequency depending on the second current, and a counter counting a number of oscillating times of the oscillation signal per a predetermined period; wherein the current converter comprises a first constant current source and output a combined current of the first constant current of the first constant current source and the first current as the second current in response to the pulse signal, so that the semiconductor device suppresses an increase circuit size.