We have investigated quantum electron transport in nanoscale double-gate MOSFETs using the multiband structure model for Si and the non-equilibrium Green function method. To obtain an accurate and realistic Si band structure, the empirical sp(3)s* tight-binding model including nearest and second-nearest neighbor coupling has been adopted. Especially, the dependence of the difference between the drain currents calculated from the present multiband and conventional effective mass models on the silicon layer thickness (t(Si)) has been examined. As t(Si) decreases below 3 rim, the current calculated from the multiband model becomes lower than that based on the effective mass model, and the difference between both currents increases. On the other hand, as t(Si) increases above 3 rim, the current from multiband structure calculations turns high compared to the current from effective mass calculations. (C) 2009 Elsevier Ltd. All rights reserved.