A semiconductor device includes a well region, a buffer region, an insulating film, an electrode, and an electric field relaxing structure. An impurity concentration in the buffer region is reduced in a direction away from the active region. An end portion of the electrode is located at a position closer to the active region than an end portion of the buffer region. The electric field relaxing structure includes a plurality of RESURF layers each surrounding the buffer region in a plan view and formed in a surface layer of the semiconductor substrate.