To provide a semiconductor IC, a wireless IC tag and a sensor which insures stable operation, can be compact/thin sized, and inhibits camouflage of sensor on temperature administration.

To solve the problem, the semiconductor IC of this invention measures the temperature based on the variation of frequency from a oscillation circuit, wherein the capacitance of the oscillation circuit is a ferroelectric substance, therefore the oscillation frequency is characteristically varied based on the varying dielectric characteristics depending on the temperature variation of the ferroelectric substance.