The equivalent oxide thickness (EOT) of high-k n-channel metal oxide semiconductor (NMOS) transistors was scaled using 3 methods, (i) reduction of the bottom interfacial layer (BIL) using NH3 interface engineering, (ii) thickness reduction of the HfO2 dielectric, and (iii) use of metal gate electrodes to minimize top interfacial growth formation and polysilicon depletion. NMOS transistors fabricated using these methods demonstrate 0.72 nm EOT using the NH3 BIL with scaled HfO2/metal gates and 0.81 nm EOT using the O-3 BIL with scaled HfO2/metal gates. Charge pumping, mobility, and device performance results of these high-k NMOS transistors is discussed. (C) 2004 The Electrochemical Society.