The equivalent circuit models for the open and short structures used in InP DHBT on-wafer testing are presented. The model topologies are physically based. The high frequency parasitics of the structures are considered in the model topologies completely. The capacitive and resistive parasitics are extracted from the low-frequency measurements of the open structure directly. Tradition physical formulations are employed to have an initially determination of the inductive and skin effect elements of the models, and further corrected by using the analytically extracted results from the low-frequency measurements of the short structure, which enables an instance accurate formulations for the test structures modeling. The models and the modeling methodology are verified using the open and short structures manufactured at a 0.5 um InP DHBT technology, excellent agreements of the model simulated and measured results are achieved over the frequency range of 0.1-325 GHz.