A trench gate MOSFET is provided. An epitaxial layer is disposed on a substrate. A body layer is disposed in the epitaxial layer. The epitaxial layer has a first trench therein, the body layer has a second trench therein, and the first trench is disposed below the second trench. A first insulating layer is disposed on a surface of the first trench. A second insulating layer is disposed in the first trench. A first conductive layer is disposed between the first and second insulating layers. A second conductive layer is disposed in the second trench. A third insulating layer is disposed between the second conductive layer and the body layer and between the second conductive layer and the first conductive layer. A dielectric layer is disposed on the epitaxial layer and covers the second conductive layer. Two doped regions are disposed in the body layer respectively beside the second trench.