We report on the responsivity of Silicon-on-Sapphire (SOS) gated photodiode. A test chip, consisting of 1024 photodetectors, connected in parallel, was fabricated in a Peregrine's 0.5μ SOS technology and successfully tested by direct photocurrent measurements. We include measurements from a test chip, showing photocurrent dependence on reverse applied voltage, incident illumination intensities and light wavelengths. Dark current measurements are also reported. The measurement results are compared with recently presented PIN photodiodes showing that the gated photodiode can be an appropriate candidate for further implementation in image sensor arrays.