This work presents a new method to extract the oxide charge densities at front (Q(ox1)) and back (Q(ox2)) interfaces of fully depleted SOI nMOSFETs. The proposed method is based on the influence of the front and back gate voltages on the back and front channel current regime, respectively. To extract Q(ox2), the drain current curve is measured as a function of the back gate voltage V-GB with the front interface inverted, When the back interface condition changes due to the back gate voltage, kinks occur in the front drain current for specific V-GB values which are used by the method. Similarly, the back drain current as a function of the front gate voltage V-GB with the back interface inverted shows some kinks for specific V-GB values which are used by the method to extract Q(ox1). MEDICI simulations were used to support the analysis and the method was applied experimentally. (C) 2002 Elsevier Science Ltd. All rights reserved.