In this paper, the channel thermal noise coefficient of Berkeley short-channel insulated gate field-effect transistor (IGFET) model 4 (BSIM4) is accurately extracted. To extract the noise coefficient of BSIM4, accurate channel thermal noise model was derived, which takes into account velocity saturation, channel length modulation, and carrier heating effects. Simplified short channel thermal noise model becomes a similar form with BSIM’s channel thermal noise model which is based on the long-channel theory. From this result we presented the methodology for extraction of the channel thermal noise coefficient. We show the extracted noise coefficient of nanoscale RF metal–oxide–semiconductor field-effect transistor (MOSFET) with L_eff = 21 nm.