Provided is a semiconductor device and a protection element capable of suppressing electrical damage to a MOSFET or the like in a semiconductor substrate. A semiconductor device according to a first aspect of the present technology includes a MOSFET as a protected element formed on a semiconductor substrate and a protection element that suppresses electrical damage to the protected element formed on the semiconductor substrate, in which the protection element includes the semiconductor substrate, one or more layers of well regions formed on the semiconductor substrate, and a diffusion layer formed on the well region. The present technology can be applied to a CMOS image sensor, for example.