This article presents an extraction method to obtain the channel thermal noise in metal-oxide-semiconductor field effect transistor (MOSFETs) directly from the de, scattering parameter and rf noise measurements. In this extraction method, the transconductance (g(m)), output resistance (R-DS), and source and drain resistances (R-S and R-D) are obtained from de measurements. The gate resistance (R-G) is extracted from scattering-parameter measurements, and the equivalent noise resistance (R-n) is obtained from rf noise measurements. This method has been verified by using the measured data of a 0.36 mu m n-type MOSFET up to 18 GHz. Comparisons between simulated and measured characteristics of noise parameters versus frequency are also presented.