The semiconductor device

The invention provides a semiconductor device capable of improving the withstand voltage and reducing the conduction resistance. The semiconductor device of one embodiment provides a MOSFET having first and second regions. The first region comprises a drain electrode of the MOSFET; a semiconductor substrate which has a first impurity concentration; a first semiconductor layer which has a second impurity concentration which is lower than the first impurity concentration; a second semiconductor layer formed on the surface of the first semiconductor layer and having a third impurity concentration which is lower than the first impurity concentration but higher than the second impurity concentration; a plurality of first trenches; a third semiconductor layer which is adjacent to the first trenches; a fourth semiconductor layer which is adjacent to the first trenches; a gate electrode layer as the gate electrode of the MOSFET; and a source electrode of the MOSFET which contacts the fourth semiconductor layer. The second region comprises a semiconductor substrate; a first semiconductor layer which has a second impurity concentration; a first insulating layer formed on the upper face of the first semiconductor layer; and a source electrode formed on the upper surface of the first insulating layer.