Since Vth of NMOS Vth=Φf+{√[2KεqNb(2|Φf|+Vsb)]}/C0 -Qtot/Co and Qtot is always positive and become dominant term, Vth of NMOS is negative in the old process. Therefore native NNMOS seems to be similar to depletion device. Or you may consider it as a always-on device.