A self-Aligned Doped Channel (SADC) is proposed and investigated for the first time. In the SADC process, the channel doping process is carried out by using solid phase diffusion from the gate; hence the doping region is fully self-aligned to the gate, and the junction capacitance can be reduced. In addition, the implantation damage in the channel is reduced. We obtained 0.25 μm gate length nMOSFETs with low noise and low power consumption by using the SADC structure. Hence, this structure is attractive for small geometry RF CMOS devices.