The impact of gate tunneling current on the on-state drive capacities and off-state standby characteristics of complementary metal-oxide-semiconductor field-effect transistors (CMOSFET's) with gate-oxide thicknesses from 3.2 to 1.2 nm was investigated. We examined optimization of nitride gate-oxide thicknesses for device performance of sub-100 nm gate-length CMOSFET's. Device design constraints on gate oxide scaling were also evaluated. Resulting predictions enable verification of nitride oxide limitations prior to replacement of gate insulators using high-permittivity material in sub-100 nm CMOSFET designs.