Abstract: A semiconductor device comprises a D.C. voltage supply region comprising a semiconductor substrate of one conductivity type having a first layer of high impurity concentration at least at its surface, and a second layer of low impurity concentration and of the same conductivity type as that of the D.C. voltage supply region, provided thereon and formed interiorly with a thin buried layer of the opposite conductivity type to that of the second layer at the vicinity of the D.C. voltage supply region. A grounding region of said opposite conductivity layer is provided in a manner to surround a specified region of the second layer and extend from the surface of the second layer to the buried layer, said surrounded specified region serving as a signal input region. In the surface of the signal input region, there is provided at least one signal output region constituting a diode together with the signal input region.