A semiconductor device including a well resistance element of high accuracy and high withstand voltage and a method of manufacturing the semiconductor device are provided.The semiconductor device includes a semiconductor substrate, a well region, an input terminal, an output terminal, a separation insulating film, and an active region. The input terminal and the output terminal are electrically coupled to the well region. The separation insulating film is arranged to be in contact with the upper surface of the well region in an intermediate region between the input terminal and the output terminal. The active region is arranged to be in contact with the upper surface of the well region. The separation insulating film and the active region in the intermediate region have an elongated shape in plan view. In the intermediate region, a plurality of separation insulating films and a plurality of active regions are alternately and repeatedly arranged.