Quantum effects are known to occur in the channel region of MOSFET devices, in which the carriers are confined in a triangular potential well at the semiconductor-oxide interface. Typically, these effects are quantified by a simultaneous solution of the Schrödinger and Poisson equations, which can be a very time consuming procedure if it needs to be incorporated in realistic device simulations. We have developed a simple and very efficient approach of approximating quantum effects by using an effective potential that takes into account the natural non-zero size of an electron wave packet in the quantized system. The benefits of the effective potential approach are that it eliminates the need for a full solution to the Schrödinger equation, thus leading to low additional computational cost. In this paper, the approach is applied in the investigation of the role of quantum-mechanical space-quantization effects in the operation of 0.1 μm MOSFET device and recently proposed SOI device structure.