A semiconductor device, including a parallel pn layer formed on a semiconductor substrate, and an insulated gate structure provided on the parallel pn layer. The parallel pn layer includes a plurality of first regions and a plurality of second regions disposed repeatedly alternating one another along a first direction that is parallel to an upper surface of the semiconductor substrate. Each of the first regions and second regions has, along the first direction, an impurity concentration that has a maximum value thereof at a peak position and that decreases gradually from the peak position. Each of the first regions and second regions has, along a depth direction thereof, a first part and a second part, a gradient of the impurity concentration along the first direction being respectively symmetrical and asymmetrical in the first part and in the second part, with respect to the peak position.