The feasibility of photonic switching of microwave signals is demonstrated for the first time using a monolithically integrated optical waveguide in silicon technology. The performance of the microwave integrated switch, illuminated either by a fiber or by the integrated optical waveguide, was measured in the 1-15 GHz waveband and was found to be identical in both cases, proving the success of the monolithic integration. The optical power required for a 3 dB commutation at 10 GHz is as low as 1 mW at a wavelength of 0.82 μm in a Silicon-On-Insulator (SOI) type structure. Higher on/off ratios were obtained from a similar device made on a bulk silicon substrate. This photoswitch may find applications in phase controlled antennas and radar systems.