The total dose radiation response of pseudo-MOS transistors fabricated in hardened and unhardened FD (fully-depleted) SIMOX (Separation by Implanted Oxygen) SOI (Silicon-on-insulator) wafers is presented.At 1 Mrad(Si) radiation dose, the threshold voltage shift of the pseudo-MOS transistor is reduced from -115.5 to -1.9 V by the hardening procedure.The centroid location of the net positive charge trapped in BOX, the hole-trap density and the hole capture fraction of BOX are also shown.The results suggest that hardened FD SIMOX SOI wafers can perform well in a radiation environment.