A bumpless monotonic bicubic interpolation (MBI) technique is proposed. The method is applied to MOSFET device modelling for guessing at a very smooth interpolated curved surface. Monotonic increase in a two-dimensional surface can be held, even if the actual device characteristics show steepest change, like punchthrough characteristics. The technique can be utilised for very small number micron and/or submicron VLSI MOSFET device modelling.