Abstract: An integrated circuit includes: a semiconductor substrate that has a well region containing a first conductivity type impurity; and an enhancement type MOS transistor and a plurality of depletion type MOS transistors, each of which is formed in the well region and has a channel region under a gate electrode. At least one of the depletion type MOS transistors has, in the channel region, an implantation region into which a second conductivity type impurity is implanted so that a threshold voltage is adjusted. The implantation region has the first conductivity type impurity and the second conductivity type impurity. Further, the second conductivity type impurity has a concentration that is higher than a concentration of the first conductivity type impurity.