An accurate method for extracting the elements of InP HBT small-signal model parameters is proposed in this paper. The method can accurately resolve the most important internal parameters from the measured S-parameters, and is not sensitive to the values of parasitic parameters. The initial values of the parasitic are extracted by using a set of test structure, and the intrinsic elements determined by using the analytical method are described as functions of the parasitic elements. The extraction procedure uses a set of closed-form expressions derived without any approximation. An experimental validation is carried out on three HBT devices and satisfactory results are obtained up to 20 GHz.