A new MOS phototransistor with high optical gain and non-destructive readout operation is proposed as a photosensor in an imaging device. The principle of this device is a conduction mechanism whereby an incident light changes the surface potential under the MOS gate and the electron current flowing in a buried channel is modulated by the surface potential. The device has a saturation exposure value of 0.1 lx·s, saturation output voltage of 500 mV at VDD=2 V, the dynamic range of 50 dB with no signal processing and non-destructive readout operation.