A spline large-signal FET model is presented. This includes a quiescent bias dependency to predict nonlinear dynamic behavior of FETs in which self-heating and trap effects are present. The intrinsic device of the model represented by a parallel connection of current and charge sources and the model parameters are extracted from bias-dependent pulsed I-Vs and S-parameters, respectively. The validity of the model is demonstrated by comparing the simulated small-signal S-parameters over a wide bias range with measured data. Nonlinear behaviors of FETs such as P-in - P-out, third-order intermodulation distortion, and efficiency are also compared.