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In this paper, we demonstrate a comprehensive analysis of small-signal source-body resistance (Rsb) effect on the RF performances of RF MOSFETs for low-cost system-on-chip (SoC) applications for the first time. Our results show that for RF MOSFETs, both the kink phenomena of S11 and S22 become more obscure as reverse body bias (VB) increases due to the decrease of transconductance (gm). In addition, an increase of source-body spacing enhances both the kink phenomena of S11 and S22, but deteriorates the current-gain cut-off frequency (fT), maximum oscillation frequency (fMAX), and RF noise and power performances due to the increase of Rsb of the devices. Analytical formulas are derived to explain the kink phenomena of S11 and S22, and to explain why increasing Rsb leads to a reduction of equivalent substrate resistance Rsub, or worse fT, fMAX, and RF noise performances of the devices. The present analyzes enable RF engineers to understand the S-parameters, noise parameters, and power performances of RF MOSFETs more deeply, and hence are helpful for them to optimize the layout of MOSFETs and to create a fully scalable RF CMOS model for SoC applications.