Semiconductor device

A semiconductor device, comprising:

• a semiconductor substrate having a first main surface and a second main surface that are opposite to each other;
• a parallel pn layer in which a plurality of first-conductivity-type regions and a plurality of second-conductivity-type regions are disposed so as to be adjacent to one another and repeatedly alternate with one another, the parallel pn layer being provided in the semiconductor substrate;
• a device structure provided between the first main surface of the semiconductor substrate and the parallel pn layer;
• a first semiconductor layer of a first conductivity type, the first semiconductor layer being provided between the second main surface of the semiconductor substrate and the parallel pn layer and having an impurity concentration that is higher than an impurity concentration of the plurality of first-conductivity-type regions;
• a second semiconductor layer of the first conductivity type, the second semiconductor layer being provided between the first semiconductor layer and the parallel pn layer and having an impurity concentration that is lower than the impurity concentration of the first semiconductor layer;
• a first electrode provided on the first main surface, the first electrode being electrically connected to the device structure;
• and
• a second electrode provided on the second main surface, the second electrode being electrically connected to the first semiconductor layer, wherein
• in a thickness direction of the second semiconductor layer from the parallel pn layer to the first semiconductor layer, the impurity concentration of the second semiconductor layer monotonically increases from a starting value equal to the impurity concentration of the plurality of first-conductivity-type regions to an ending value equal to the impurity concentration of the first semiconductor layer.