We have investigated the role of quantum mechanical space-quantization effects on the operation of a narrow-width SOI device structure. The presence of a two-dimensional carrier confinement gives rise to larger average displacement of the carriers from the interface proper and lower sheet electron density in the channel region. This, in turn, results not only in a significant increase in the threshold voltage but also in its pronounced channel width dependency. In this work, we have used classical 3D Monte Carlo particle-based simulations. Quantum mechanical space-quantization effects have been accounted for via an effective potential scheme that has been quite successful in describing bandgap widening effect and charge set back from the interface.