An analytical expression for the sheet density of induced electrons in channels of symmetric and asymmetric double-gate (DG) silicon-on-insulator (SOI) MOSFETs in a subthreshold region has been developed. A new approach for approximating the vertical electric-field in the silicon layer enabled the simple expression for electron density to be derived. This model was found to be useful for devices with wide ranges of silicon-layer thickness and channel-impurity concentration.