A semiconductor device includes a semiconductor layer. The semiconductor layer has bottom and upper surfaces opposite to each other in a first direction. The semiconductor layer includes a first region of a first conductivity type at the bottom surface, a second region of the first conductivity type at the bottom surface surrounding the first region, a third region of the first conductivity type above the first and second regions, and a fourth region of a second conductivity type extending from the upper surface into the third region. In a first cross sectional plane along the first direction, an outer edge of the first region is within an outer edge of the fourth region by a first distance. In a second cross sectional plane along the first direction, an outer edge of the first region is within an outer edge of the fourth region by a second distance.