Provided is a semiconductor device in which movable ions in an insulation layer on a main surface are reduced and dielectric strength is enhanced. A semiconductor device has a plurality of FLRs, an insulation layer, and a semiconductor layer. The plurality of FLRs surrounds, in a plan view of a substrate, an active region in which an element is formed. The insulation layer is provided on the main surface of the semiconductor device and covers the plurality of FLRs. The semiconductor layer is provided in the insulation layer and surrounds the active region in parallel to the FLRs. The semiconductor layer contains impurities at a surface density lower than a surface density that satisfies a RESURF condition. In the plan view, the semiconductor layer overlaps with a part of the region (an inter-ring region) between adjacent FLRs and does not overlap with rest of the inter-ring region.