An integrated circuit containing an analog MOS transistor has an implant mask for a well which blocks well dopants from two diluted regions at edges of the gate, but exposes a channel region to the well dopants. A thermal drive step diffuses the implanted well dopants across the two diluted regions to form a continuous well with lower doping densities in the two diluted regions. Source/drain regions are formed adjacent to and underlapping the gate by implanting source/drain dopants into the substrate adjacent to the gate using the gate as a blocking layer and subsequently annealing the substrate so that the implanted source/drain dopants provide a desired extent of underlap of the source/drain regions under the gate. Drain extension dopants and halo dopants are not implanted into the substrate adjacent to the gate.