The effects of fluorine ion implantation on the formation and characteristics of SOI/SIMOX structure have been investigated by the combined implantation of high dose oxygen and lower dose fluorine into silicon. After high temperature annealing, fluorine atoms migrated to the Si surface, showing an anomalous out-diffusion behavior. The SOI structure is very different from that of non-fluorinated samples. A polycrystalline silicon layer was formed between the silicon overlayer and the buried oxide. Furthermore, the lower energy F+ implantation affected the SOI structure more significantly and a Si-rich layer was formed in the buried oxide. The electrical properties of the silicon overlayer were analyzed by spreading resistance probe and Hall measurements.