Abstract: An impedance matching circuit is provided. The present impedance matching circuit is able to match impedance using a transformer which is arranged inside a dielectric substrate and arranged to overlap with a bonding pad area and an end of a transmission line, thereby enabling transmitting signals at a desired frequency with a minimum insertion loss without using a very thin transmission line which is several to dozens of ?m wide or specially designed antennas in order to compensate for inductance. Thus, the present impedance matching circuit may be applied to various millimeter bands.