Silicon-controlled rectifier (SCR) had been reported with good electrostatic discharge (ESD) robustness and low parasitic capacitance. In this work, SCR devices were investigated to have low and constant capacitance for on-chip ESD protection in RF ICs. The test devices had been verified in a 65-nm fully-silicided CMOS process. The SCR devices can pass 8-kV human-body-model (HBM) ESD tests, and the parasitic capacitance at 5 GHz kept at ∼135 fF with only 3-fF variation as the input voltage swung from VSS to VDD. Thus, the ESD protection design with SCR devices is very suitable for RF ESD applications.