In this work NMOSFETs were fabricated on both the standard SIMOX material and SIMOX material which was implanted with Si⁺ into the buried oxide(BOX). The purpose of this paper is to show the influence of Si⁺ implantation on total-dose radiation response of SOI MOSFETs. The total-dose radiation response experimental results of NMOSFETs fabricated on both materials were compared and discussed, which indicated that the degradation of electrical characteristics of the NMOSFETs under total-dose irradiation was improved greatly corresponding to the SIMOX material with implanted Si⁺. The front gate leakage current of the NMOSFETs increased much less than the control ones with the increase in radiation dose.The back gate threshold voltage shifts of the NMOSFETs were much smaller than the control ones under different total-dose. The analyses of the I-V characteristics of the devices indicated that the implantation of Si⁺ introduced electron traps which compensated the intrinsic hole traps in the BOX and reduced the net trapped charge generated during the radiation, thus greatly improving the total-dose radiation tolerance of the devices.