Abstract: A semiconductor device with different gate structures and a method of fabricating the same are disclosed. The a method includes forming a fin structure on a substrate, forming a thermal oxide layer on top and side surfaces of the fin structure, forming a polysilicon structure on the thermal oxide layer, doping portions of the fin structure uncovered by the polysilicon structure to form doped fin portions, forming a nitride layer on the polysilicon structure and the thermal oxide layer, forming an oxide layer on the nitride layer, doping the nitride layer with halogen ions, forming a source/drain region in the fin structure and adjacent to the polysilicon structure, and replacing the polysilicon structure with a gate structure.