Semiconductor integrated circuit

A semiconductor integrated circuit comprising:

• a signal input terminal to which an input signal is applied;
• at least one protection element connected between at least one of voltage supply terminals of source and reference voltages and the input terminal;
• and
• a protected circuit which is connected to the input terminal via a coupling capacitance, wherein
• the protected circuit and protection element are formed on the same semiconductor substrate,
• the protection element includes two diodes having their anodes connected together to form a floating node and two cathodes connected to the protected circuit,
• the two diodes are formed in a well-in-well structure on the semiconductor substrate, and
• the well-in-well structure includes
• a P-type well forming the floating gate,
• an N-type well which surrounds the surfaces of the P-type well other than that on the front side of the substrate with the deep portion side of the substrate so as to form the cathode of one of the diodes, and
• a first N-type region formed in the P-type well so as to form the cathode of the other diode.