| 摘要 |
PURPOSE: To provide a semiconductor device such as a power MOSFET capable of reducing ON resistance by effectively lowering drift resistance components. CONSTITUTION: The semiconductor device is provided with a first conductivity type drain layer (12), a first conductivity type drift layer (8) on it, a second conductivity type base layer (10) on it, a first conductivity type source region (16) on it, and a trench gate provided with a gate insulation film (2) and a gate electrode (4) formed on the inner wall surface of a trench (T) to the drift layer through the base layer. The gate insulation film (2) is formed thicker at a part adjacent to the drift layer than at a part adjacent to the base layer. The drift layer (8) is provided with density gradation that a first conductivity type impurity density rises as approaching the drain layer along the depthwise direction of the trench near the drain layer.
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