Direct and Fowler-Nordheim tunneling through ultra-thin gate dielectrics is modeled based on an approach for the transmission coefficient (TC) of a potential barrier that is modified by the image force. Under the constraint of equal actions the true barrier is mapped to a trapezoidal pseudobarrier resulting in a TC very close to the numerical solution of the Schro¨dinger equation for all insulator thicknesses and for all energies of the tunneling electron. The barrier height of the pseudopotential is used as a free parameter and becomes a function of energy in balancing the actions. This function can be approximated by a parabolic relation which makes the TC of arbitrary barriers fully analytical with little loss of accuracy. The model was implemented into a multidimensional device simulator and applied to the self-consistent simulation of gate currents in metal-oxide-semiconductor (MOS) capacitors with gate oxides in the thickness range 15 Å–42 Å. Excellent agreement with experimental data was obtained using a thickness-independent tunnel massmox=0.42 m0. Thanks to the CPU-time efficiency of the method the simulation of a complete MOS-field-effect-transistor with dominating gate current becomes possible and shows the potential for further applications. ©1997 American Institute of Physics.