Disclosed are methods of forming bulk FinFET semiconductor devices to reduce punch through leakage currents. One example includes forming a plurality of trenches in a semiconducting substrate to define a plurality of spaced-apart fins, forming a doped layer of insulating material in the trenches, wherein an exposed portion of each of the fins extends above an upper surface of the doped layer of insulating material while a covered portion of each of the fins is positioned below the upper surface of the doped layer of insulating material, and performing a process operation to heat at least the doped layer of insulating material to cause a dopant material in the doped layer to migrate from the doped layer of insulating material into the covered portions of the fins and thereby define a doped region in the covered portions of the fins that is positioned under the exposed portions of the fins.