This paper presents for the first time a method to directly calculate the noise parameters (minimum noise figure NFmin, equivalent noise resistance R-n, and optimized source resistance R-opt and reactance X-opt) of MOSFETs based on HSPICE level 3 mode!, All physically-based high frequency noise sources - thermal noise from the channel, gate, source and drain resistances, induced gate noise and their correlations are considered, and the impact of gate resistance and induced gate noise on the noise parameters are studied. The method of direct calculation of noise parameters can be applied to any small signal device model.