Quantum effects have been reported to play an important role in the operation of narrow width SOI devices, in which the carriers experience a two dimensional confinement in a square quantum well at the semiconductor-oxide interface. This results not only in a significant increase in the I threshold voltage but also in its pronounced channel width dependency. Typical method to simulate these effects is a simultaneous solution of the Schrödinger and Poisson equations, which can be a very time consuming procedure. An alternative way is to use the recently developed effective potential approach that takes into account the natural non-zero size of an electron wave packet in the quantized system. In this work, we have applied the effective potential approach in a recently proposed SOI device structure to quantify these effects. In a second effort we utilize the Landauer's formalism to calculate the on-state current quantum mechanically and estimate the increase in device threshold voltage due to the lateral quantization.