A dielectric material layer is formed on a bottom surface and sidewalls of a trench in a semiconductor substrate. The silicon oxide layer forms a drift region dielectric on which a field plate is formed. Shallow trench isolation may be formed prior to formation of the drift region dielectric, or may be formed utilizing the same processing steps as the formation of the drift region dielectric. A gate dielectric layer is formed on exposed semiconductor surfaces and a gate conductor layer is formed on the gate dielectric layer and the drift region dielectric. The field plate may be electrically tied to the gate electrode, may be an independent electrode having an external bias, or may be a floating electrode. The field plate biases the drift region to enhance performance and extend allowable operating voltage of a lateral diffusion field effect transistor during operation.