The equivalent circuit models for the open and short structures used in InP DHBT on-wafer testing are presented. The model topologies were physically based. The high frequency parasitics of the structures were considered in the model topologies completely. The capacitive and resistive parasitics were extracted from the low frequency measurements of the open structure directly. Tradition physical formulations were employed to have an initial determination of the 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 accurate formulation for the test structures modeling. The models and the modeling methodology were verified using the open and short structures manufactured in a 0.5 μm InP DHBT technology. Excellent agreements of the model simulated and measured results are achieved over the frequency range of 0.1~325 GHz.