A quantum mechanical treatment of electron inversion layers is incorporated in the hydrodynamic (HD) transport model used in UT-MiniMOS. A physically based, yet computationally efficient, three-subband model is implemented in the HD simulation tool. The three-subband model, which is based upon solutions to Schrodinger's equation, has the important advantage of more accurately predicting the distribution of electrons in the inversion layers than does more conventional classical models. A more simplified quantum mechanical model with carrier heating effects included has also been developed. Terminal currents are calculated using these quantum mechanical models and the comparison with results from classical calculations indicates the importance of quantum mechanical effects in the deep submicron device simulations.