Metal-oxide-semiconductor (MOS) devices have been used for detecting low-energy (2 to 20 keV) x rays for incident fluences of 10-4 to 10-1 cal/cm2 (or dosage in the device of 103 to 106 rads) in a bent-crystal spectrometer application. An attractive feature of the detector is that the three functions of 1) detection, 2) memory, and 3) readout are integrated into one semiconductor chip.