We present a physically based, accurate model of the direct tunneling gate current of nanoscale metal-oxide-semiconductor field-effect transistors considering quantum mechanical effects. Effect of wave function penetration into the gate dielectric is also incorporated. When electrons tunnel from the metal oxide semiconductor inversion layer to the gate, the eigenenergies of the quasi-bound states turn out to be complex quantities. The imaginary part of these complex eigenenergies, Γij, are required to estimate the finite lifetimes of these states. We present an empirical equation of Γij as a function of surface potential. Inversion layer electron concentration is determined using eigenenergies, calculated by modified Airy function approximation. Hence, a compact model of direct tunneling gate current is proposed using a novel approach. Good agreement of the proposed compact model with self-consistent numerical simulator and published experimental data for a wide range of substrate doping densities and oxide thicknesses states the accuracy and robustness of the proposed model. The proposed model can well be extended for devices with high-κ/stack gate dielectrics introducing necessary modifications. Copyright © 2011 John Wiley & Sons, Ltd.