Disclosed herein is a power amplifier. The power amplifier includes a first common source transistor for amplifying an input signal into a predetermined level, a second common source transistor for compensating for input capacitance and performing auxiliary amplification for the first common source transistor, and a common gate transistor connected to the first common source transistor in a cascode structure, configured to be connected in parallel to the second common source transistor and prevent the first common source transistor from breaking down, and configured to output a signal amplified by a value obtained by adding the gain of the first common source transistor and the gain of the second common source transistor to each other.