In this paper, a new compact charge based DC model for the drain current of long channel fully depleted ultra-thin body SOI MOSFETs and asymmetric double-gate MOSFETs with independent gate operation (ADGMOSFETs) is presented. The model was validated by both TCAD simulations and electrical measurements with a good agreement. In particular, great care was taken during the derivation of the model in order to respect the physics of the device and to make the correct approximations. The obtained solutions can be viewed as a generalization of classical MOS theory to the case of undoped fully depleted ADGMOS. As a result, the model consists of relatively simple equations and is a promising approach for the compact modeling and parameter extraction of fully depleted SOI transistors. (C) 2010 Elsevier Ltd. All rights reserved.