The significance of the nonlinearity of HEMT capacitance models to the prediction of intermodulation is investigated. Three capacitance models, one linear and two with contrasting nonlinear behavior, are shown to exhibit almost identical performance. It is concluded that the nonlinearity of the low-frequency model is the dominant distortion generating component. Development of capacitance models with accurate high-order derivatives is unwarranted without an accurate dc model. Therefore, careful characterization of the drain current description is most important for the successful circuit simulation.