A semiconductor integrated circuit includes a substrate of a first conductivity type, and a first MOS transistor and a second MOS transistor both formed in the substrate. The first MOS transistor includes first drain and first source regions as first active regions of a second conductivity type; a second active region of the first conductivity type; a first gate electrode disposed between the first drain and source regions; and a first substrate electrode connected to the second active region. The second MOS transistor includes a second drain region and a second source region which are formed between the first source region and the second active region, such that the first source region is proximate to the second drain region. The first substrate electrode is electrically separated from the first drain and source electrodes, and the second MOS transistor is connected between the first substrate electrode and the first source electrode.