A dual trench MOS transistor comprises of the following elements. A plurality of trenches are formed in an n− epitaxial layer on a heavy doped n+ semiconductor substrate and spaced to each other by one mesa. Each the trench has a trench oxide layer formed on a bottom and sidewalls thereof. A first polysilicon layer is formed in the trenches. A plurality of recesses are formed in the mesas and spaced to each other with one sub-mesa. Each the recess has a recess oxide layer formed on a bottom and sidewalls thereof. A second polysilicon layer for serving as a gate is formed in the recesses. The mesas are implanted to have implanted areas at two side of the gate. The implanted areas and the first polysilicon layer are applied to serve as the source. The rear surface of the substrate is served as the drain.