We report the experimental resutls on AlGaAs/GaAs heterojunction bipolar transistors (HBTs) with carbon-doped base structure. To characterize the output power, load-pull mehtod was employed. By characterizing the devices with HP8510C, we extracted the small-signal equivalent circuit. The HBTs were fabricated employing wet mesa etching and lift-off process of ohmic metals. the implementation of polyimide into the fabriction process was accomplished to obtain the lower dielectric constant resultig in significant reduction of interconnect routing capacitance. The fabricated HBTs with an emitter area of 6${ imes}14{mu}m^{2}$ exhibited current gain of 45, BV$_{CEO}$ of 10V, cut-off frequency of 30GHz and power gain of 1 3dBm. To extract the small signal equivalent circuit, the de-embedded method was applied for parasitic parameters and the calculation of circuit equations for intrinsic parameters.