A transistor includes a semiconductor layer, and a gate dielectric is formed on the semiconductor layer. A gate conductor is formed on the gate dielectric and an active area is located in the semiconductor layer underneath the gate dielectric. The active area includes a graded dopant region that has a higher doping concentration near a top surface of the semiconductor layer and a lower doping concentration near a bottom surface of the semiconductor layer. This graded dopant region has a gradual decrease in the doping concentration. The transistor also includes source and drain regions that are adjacent to the active region. The source and drain regions and the active area have the same conductivity type.