This work presents a new method to extract the silicon film and front oxide thickness on fully depleted silicon-on-insulator nMOSFETs. The proposed method exploits the influence of the front/back gate voltages on the back/front channel current regime. To extract the silicon film thickness, 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 biases and these are used by the method. Similarly, the back drain current as a function of the front gate voltage V-GF With the back interface inverted shows some kinks at specific V-GF, which are used by the method to extract the front oxide thickness. MEDICI simulations were used to support the analysis and the method was validated experimentally.