The influence on the base-collector junction capacitance Cbc of the energy band structure of the InP heterojunction bipolar transistors is researched. A physical model of small-signal InP double heterojunction bipolar transistor （DHBT） is developed, which takes into account the base-emitter and collector-emitter metalisations by using two additional capacitances Cmb and Cmc. The resistance of the model is divided into the intrinsic resistance, the extrinsic resistance and the parasitic resistance. Meanwhile, a physically meaningful small-signal parameter extraction procedure for the model is presented, in which all the equivalent circuit elements are extracted without reference to numerical optimization. An experimental validation is carried out, and excellent results are obtained over a wide range of bias points, which demonstrates good modeling accuracy.