A semiconductor device which can reduce a noise current without depending upon the mounting layout of a circuit board by matching the impedance of the power supply line and that of the GND line in the semiconductor device. In a typical embodiment of this invention, the semiconductor device having a package substrate, a semiconductor chip, a power supply line and a GND line is further provided with a conduction board and first and second impedance adjustment elements. The conduction board determines the parasitic capacitance of the power supply line and the GND line, and the first and second impedance adjustment elements adjust the impedance of the power supply line and the GND line.