High gate leakage current, as a central problem, has decelerated the downscaling of minimum feature size of the field effect transistors In this paper, a combination of density functional theory and non equilibrium Green’s function formalism has been applied to the atomic scale calculation of the tunnel currents through CeO2, Y2O3, TiO2 and Al2O3 dielectrics in MOSFETs. The tunnel currents for different bias voltages applied to Si/Insulator/Si systems have been obtained along with tunnel conductance v/s bias voltage plots for each system. The results are in agreement to the use of high dielectric constant materials as gate dielectric so as to enable further downscaling of MOSFETs with reduced gate leakage currents thereby enabling ultra large scale integration. When used as dielectric, TiO2 exhibits extremely low tunnel currents followed by Y2O3 while CeO2 and Al2O3 exhibit high tunnel currents through them at certain bias voltages.