A charge sheet model is proposed to analyze the transistor characteristics of fully depleted SOI four gate field effect transistors (G(4)-FETs). The model is derived assuming a parabolic potential variation between the junction-gates and by solving 2-D Poisson's equation. The proposed model facilitates the calculation of surface potential and charge densities as a function of all gate biases. Modifying this charge sheet model for non-equilibrium condition, current-voltage and capacitance-voltage characteristics are also analyzed. Different back surface charge conditions are considered for each analysis. The models are compared with 3-D Silvaco/Atlas simulation results which show good agreement. (C) 2013 Elsevier Ltd. All rights reserved.