A two-dimensional (2D) numerical simulation code of drain current including self-consistent solving of the Schrödinger and Poisson equations coupled with the drift-diffusion transport equation in double-gate (DG) metal–oxide–semiconductor field-effect transistor (MOSFET) devices has been developed. This code has been used to investigate the operation of independent DG (IDG) MOSFETs compared with classical DG MOSFETs in terms of short-channel effects (SCEs) and carrier quantum confinement. Simulations show that IDG MOSFET operation is different from that of DG MOSFETs due to the presence of a transverse electric field in the first structure that induces significant enhancement of quantum mechanical confinement. This leads to subthreshold performance degradation and to SCE enhancement in IDG MOSFETs compared with DG MOSFETs. We show that, in contrast to DG MOSFETs, quantum confinement effects must be taken into account in IDG MOSFET operation even for thick silicon films (>10 {15 nm).