Abstract: In this paper, a new algorithm is introduced to build microwave FET large signal model. Using a principal component sensitivity analysis procedure, this algorithm transforms the axes from model parameters to the uncorrelated principal component axes, then carries on I - V characteristic curve fitting by the L-M method. The results show that this algorithm is very fast and accurate. Using this algorithm, we develop a program for extracting model parameters. Eight large signal FET models have been considered and have been compared for four different cases. They can provide the microwave circuit designers with a practical benchmark.