Provided are a semiconductor element and a semiconductor device capable of achieving on-resistance reduction and miniaturization. The semiconductor element is used in a semiconductor switch for protecting an electric circuit, and includes a semiconductor substrate SB, a MOS transistor Tr provided on the semiconductor substrate SB, and a source electrode SE provided on a front surface 2a side of the semiconductor substrate SB. The MOS transistor Tr includes an n-type source region 8 connected to the source electrode SE, an n-type drift region 21 arranged away from the source region 8, and a p-type well region 31 arranged between the source region 8 and the drift region 21. The source region 8 is interposed between the source electrode SE and the well region 31.