||Trench Double-diffused Metal-Oxide-Semiconductor Field-Effect Transistor (DMOSFET) is a special class of discrete power transistor. It is recognized by its ultra-low on-resistance, due to its special device structure of employing vertical trenches for channel formation. The inversion and accumulation layer mobilities of the trench DMOSFET are important parameters to determine its on-resistance. Extraction of the mobilities is difficult because the carrier flow in the trench DMOSFET is going through different regions in addition to the channel region. Existing approaches for the extraction of the mobilities suffer from different kinds of discrepancies arising from simulations, use of test structures, or incomplete consideration of all the carrier flow regions. Furthermore, they can be used to extract the inversion layer mobility only, but not the accumulation layer mobility as well. In this thesis, a simple method is proposed and implemented to extract both the inversion and accumulation layer mobilities of electrons in n-channel trench DMOSFETs. First, a new model is developed for the on-resistance of the n-channel trench DMOSFET. The proposed on-resistance model is fitted to the experimental data measured from an experimental n-channel trench DMOSFET by the method of linear least-squares fitting. A very good fit is obtained such that the average percentage error between the model curve and the experimental on-resistance is less than 1 %. The parameters obtained from the fitting are used to calculate the inversion and accumulation layer mobilities as a function of a wide range of effective electric field. The calculated mobilities agree very well with those previously reported for conventional MOSFETs.