Field effect transistor having a multi-width electrode structure and method for manufacturing the same

A field effect transistor is manufactured by firstly forming an epitaxial layer on a substrate. Then, a trench having an oxide layer is formed on the epitaxial layer. The oxide layer has a first electrode portion having a first width and a first height and a second electrode portion having a second width and a second height. A gate oxide layer covering the oxide layer and the second electrode portion has a gate portion having a third width. The epitaxial layer has a body region and a source region, where these two regions are adjacent to the gate portion and covered by an interlayer dielectric. A source electrode covering the body region and the interlayer dielectric contacts the source region. The first height is no less than the second height, the first width is smaller than the second width, and the second width is smaller than the third width.