To provide a semiconductor device, a power conversion device, and a method for manufacturing the semiconductor device, in which unevenness in short circuit capacity is suppressed.SOLUTION: A semiconductor device comprises: a substrate; a first conductivity type drift layer provided on an upper surface side of the substrate; a second conductivity type well region provided on an upper surface side of the drift layer; a first conductivity type source region provided on an upper surface side of the well region; a channel region which is a part of the well region and sandwiched between the drift layer and the source region; a gate oxide film provided on an upper surface of the drift layer; a gate electrode provided on the gate oxide film; a source electrode connected to the source region; and a drain electrode provided on a rear surface of the substrate. In the source region, a thin wall part thinner than the circumference is provided between a portion adjacent to the channel region and a portion to which the source electrode is connected.SELECTED DRAWING: Figure 1
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