A Physical Unclonable Function (PUF) semiconductor device includes a semiconductor substrate, and regions, with implant regions and covered regions, in the semiconductor substrate. A hardmask covers a first covered region and a second covered. The first implant region having a first concentration of ions, and at least one second implant region having a second concentration that is less than the first concentration. First and second FETs are formed on the regions. The first and second FETs have a voltage threshold mismatch with respect to one another based on the first region and the at least one second region.