We calculate the normalized electron wave functions in the inversion layers of nMOSFETs with ultra-thin gate oxides using an asymptotic boundary condition that considers flat energy band profile deep inside the 'metal' as well as deep inside the semiconductor. Comparison of our results with those calculated using the conventional boundary condition that forces the wave functions to zero at the semiconductor-oxide interface shows that the use of the conventional boundary condition overestimates the distance of the carriers from the interface by a few angstroms.