A power semiconductor device has a semiconductor body which includes an active area and a peripheral area which both define a horizontal main surface of the semiconductor body. The semiconductor body further includes an n-type semiconductor layer, a pn junction and at least one trench. The n-type semiconductor layer is embedded in the semiconductor body and extends to the main surface in the peripheral area. The pn junction is arranged between the n-type semiconductor layer and the main surface in the active area. The at least one trench extends in the peripheral area from the main surface into the n-type semiconductor layer and includes a dielectric layer with fixed negative charges. In the vertical direction, the dielectric layer is arranged both below and above the pn junction. The dielectric layer with fixed negative charges typically has a negative net charge. Further, a method for forming a semiconductor device is provided.