In this work we investigate the effect of quantization at the polysilicon/oxide interface on the properties of n- and p-MOS transistors. As a consequence of the potential energy barrier, a dark space depleted of free carriers is created at the interface, which is slightly dependent on the applied bias. Both polysilicon capacitance and voltage drop in all regions of operation of modern MOS devices are dominated by quantum effects. Polysilicon quantization leads to a reduction in the gate capacitance in the same way as substrate quantization, and to a negative voltage shift, which is opposed to conventional substrate quantization. These effects are discussed in detail for dual-gate MOSFET's with ultra-thin oxides. (C) 2002 Elsevier Science Ltd. All rights reserved.