The radiation response of SiO2 gate oxides grown on 4H-SiC to NO passivation is presented for the first time. The effects of gamma radiation on Q(eff) are similar for n-4H-SiC MOS capacitors both with and without NO passivation, but are different in sign (negative) compared to SiO2 on Si. The variation in D-it with total dose, however, is different for the passivated versus the unpassivated samples. Comparisons between Si Sol and 4H-SiC suggest that properly passivated SiC MOSFETs should have good radiation tolerance. (C) 2002 Elsevier Science Ltd. All rights reserved.