The stability to proton radiation of GaN metal oxide semiconductor (MOS) diodes fabricated using the novel gate dielectric Sc2O3 was investigated. The MOS diodes were fabricated by depositing the dielectric with molecular beam epitaxy onto MOCVD-grown GaN on sapphire. The stability of GaN Schottky diodes was also investigated for comparison. Current-voltage (I-V) and capacitance-voltage (C-V), were employed to monitor any change in the electrical characteristics of the diodes. Preliminary testing indicates that the GaN-based diodes are in fact affected by proton irradiation, but only at fairly high doses. Doses equivalent to 10 years in low earth orbit, ~5x109cm-2, produce a decrease in the reverse breakdown field in both Schottky and MOS diodes. However, even after irradiation, the GaN MOS diodes showed twice the reverse breakdown voltage of non-irradiated Schottky diodes. Further, while the Schottky diodes showed reduced forward breakdown voltage, the MOS diodes showed no change in forward breakdown. These results suggest that the oxide/GaN interface is stable and is not being damaged by the radiation. The change in reverse breakdown is most likely due to generation of damage in the GaN resulting in the formation of shallow donors.