A structure with floating electrodes in the trench sidewall oxide layer of shielded gate trench MOSFET (SGT structure) is proposed to optimize the specific on-resistance and the specific gate-drain capacitance by improving the electric field distribution. Based on the conventional SGT structure, the floating electrode structure with a breakdown voltage of 141.1 V, a specific on-resistance of 55 mΩ·mm2 and a specific gate-drain capacitance of 4.72 pF·mm-2 is finally obtained by increasing the doping concentration of the epitaxial layer, and changing the length and position of the floating electrodes and the thickness of the oxide layer. Compared with the SGT structure with the same structural parameters, the specific on-resistance of the floating electrode structure is decreased by 9.3%, the Baliga’s figure of merit is increased by 13%, and the specific gate-drain capacitance is decreased by 28.4% under the same breakdown voltage.