An analytical parameter-extraction method for pi-type substrate resistance model of RF MOSFETs based on three-port measurement is presented for the first time. The values of substrate resistance components are extracted directly from the three-port S-parameter measurement data, and the output admittance of the MOSFETs is well matched up to 110 GHz. Using a macromodel with extracted substrate components, it is verified that pi-type substrate resistance model is more accurate than other substrate resistance models