Total dose effects in composite nitride-oxide (NO) films with various nitride and oxide thicknesses are studied. Metal nitride oxide semiconductor (MNOS) devices with thicknesses in the range of power transistors have been irradiated with X-rays up to a total dose of 1 Mrad (SiO2). A model is proposed to describe the observed flatband voltage shifts as a function of total dose in the range of electric fields where the charge yield in the dielectrics to a first order approximation is linearly proportional to the electric field. The modulation of electric field in the dielectrics due to charge accumulation at the NO interface is found to be the dominating factor in determining the flatband voltage shift. It is suggested that, for the process conditions examined here, n-channel MNOS devices with oxide thickness between 12 and 15 nm give minimal radiation-induced flatband voltage shifts. (C) 2002 Published by Elsevier Science Ltd.