The use of an impurity doped silicon MOSFET as an infrared detector (IRFET) has recently been proposed. This report gives a description of the operation of this new type of infrared detector and provides experimental verification of the design. The IRFET is an integrating static read only memory element whose conductance is modulated by infrared radiation. Operation has been observed and characterized using the gold acceptor level and gold donor level in the near infrared wavelength range from 1.0 to 3.0 microns. It will be shown from pulsed capacitance measurements on MOS capacitors and from measurement of the IRFET response that the characteristics of the gold impurity center in the surface space charge region correspond to the results observed previously for the center in bulk silicon. Operation of the IRFET can then be described on the basis of a simple model where the change in charge state of the impurity center in the surface space charge region due to photoionization modulates the threshold voltage of the MOSFET and thus conductance of the device.