Abstract We describe a metal-oxide silicon (MOS) phototransistor that relies on a novel lateral doping scheme that creates a p–i–n junction configuration for light detection. This is essentially a hybrid device with the horizontal structure of a p–i–n diode and the vertical structure of a MOS field-effect transistor. The lateral p–i–n diode detects light whereas the gate can be used to change the current flowing through the device; making it appear as a MOSFET. This feature makes it easy to integrate it with other conventional MOSFETs on a CMOS process flow. The device shows high optical responsivities that persist to wavelengths in the near-ultraviolet region. The fabrication of the device as well as its electrical and optical characteristics is described.