In this paper we report radiation effects in radiation-hardened power VDMOSFET devices with different cell structures (stripe-cell and hexagonal-cell) at various irradiation doses of X-ray (45 kV acceleration voltage) by means of DCIV measurements as well as sub-threshold methods, and observed that radiation damages are closely related to cell geometry of the chips. Both radiation-induced oxide charges and interface traps in the chips with stripe cell are smaller than those with hex cell under the same irradiation dose because they have different stresses in the cells. Moreover, the recombination current peaks show a saturation feature when X-ray irradiation dose come to about 4 Mrads (from ∼4 to 14.4 Mrads) in the radiation-hardened samples.