Silicon-controlled rectifier (SCR) has been reported with the good electrostatic discharge (ESD) robustness under the lower parasitic capacitance among ESD devices in CMOS technology. To correctly predict the performances of SCR-based ESD-protected RF circuit, it is essential for RF circuit design with accurate model of SCR device. The small-signal model of SCR in RF frequency band is proposed in this work. The measured parasitic capacitances well agree with the simulated capacitances. With the proposed small-signal model, on-chip ESD protection can be co-designed with RF circuits to eliminate the negative impacts caused by ESD protection SCR on RF performances.