HfSiON gate dielectrics are fabricated by oxidation of co-sputtered Hf and Si, followed by nitridation with NH 3 gas. It is found that HfSiO film stays in an amorphous state after oxidation, while HfO 2 film tends to crystallize. Due to its thermally robust properties of HfSiON, lower gate leakage and good uniformity are achieved even after high thermal treatment (above 1000 °C). A reduction in capacitance due to lower permittivity is compensated by the introduction of a Ni-FUSI electrode, where improved inversion capacitance leads to a higher on-state drive current.