Semiconductor amplifier circuit

A semiconductor amplifier circuit comprising:

• a semiconductor substrate of one conductivity type;
• a well region of the one conductivity type, formed in said semiconductor substrate;
• a well region defining region of the other conductivity type, including a side wall portion and a bottom portion defining said well region;
• a first transistor formed in said well region;
• and
• a second transistor formed on a surface of another portion of said substrate other than a portion on which said well region is formed, wherein, during said first and second transistors are in operation, a potential of said substrate is set to a reference potential, a potential of said well region defining region is set equal to the potential of said substrate or set to a value at which a junction between said well region defining region and said substrate is reverse-biased and at least one of electrodes of said first transistor is set to a potential at which a junction between said well region defining region and said well region is reverse-biased and electrode potentials of said first and second transistors are set such that one of said first and second transistors operates with a potential not lower than the reference potential, at least one of electrodes of the other of said first and second transistors is set to a potential lower than the reference potential such that the other transistor operates with a potential lower than the reference potential.