Semiconductor device

A semiconductor device with MOS FET circuits, comprising:

• a semiconductor substrate having one conductivity type;
• an insulation layer formed on said substrate;
• an active portion formed in said substrate and coupled to the MOS FET circuits;
• an input protection resistor, having one end coupled to said active portion, formed on said insulation layer;
• a bonding pad, connected to another end of said input protection resistor, formed on said insulation layer;
• an impurity diffusion region having an opposite conductivity type relative to said one conductivity type formed underlying said insulation layer, said impurity diffusion region positioned at least under said input protection resistor and electrically maintained at floating potential level;
• and
• a channel stopper region having said one conductivity type and a higher impurity concentration than that of said substrate, formed underlying said insulation layer, said channel stopper region positioned at the surface portion of said semiconductor substrate except for the portion where said impurity diffusion region is formed;
• wherein said insulation layer overlying said impurity diffusion region is not thicker than that of said insulation layer overlying said channel stopper region and when a voltage of a predetermined polarity is applied across the bonding pad, the insulating layer and the substrate, a depletion layer is formed between said impurity diffusion region and the substrate such that the applied voltage is divided by the insulating layer and the depletion layer thereby to reduce the voltage existing across the insulating layer.