Abstract: A total dose radiation hardened power VDMOS device is fabricated by growing the thin gate SiO2 after the P-body diffusion and using a double passivation layer (Si3N4-SiO2). The experimental results are presented and fit 2D simulation. For the specified power VDMOS device, the threshold voltage shifts is only -1 V at a x-ray total dose of 972×103 rad (Si). It is demonstrated that the total dose radiation tolerance of the power VDMOS device are improved significantly.