Abstract: A PIN switch with harmonic cancellation circuit is proposed for the situation that PIN switch induces harmonic signal at high power. The harmonic cancellation circuit is composed of a reverse paralleling PIN diode. Based on theoretical analysis, the experimental circuit is developed and measured. The result shows that the second harmonic is smaller than -63. 5 dBc which is 14 dB better than before when frequency is 1-1.2 GHz and input power is smaller than 45 dBm. This harmonic cancellation circuit can effectively suppress the second harmonic.