In this paper, a nanowire germanium/gallium arsenide (Ge/GaAs) heterojunction-based tunneling field-effect transistor (TFET) is investigated, with an emphasis on the device-circuit interaction. It is applied to a common-source (CS) amplifier, one of the most fundamental analog circuit blocks, and its performance is evaluated with a device-circuit mixed-mode simulation. Furthermore, the passive elements are adjusted to obtain the proper operating point (Q-point) of the circuit, and high-frequency operations are evaluated on this basis. Moreover, from the simulation results, the transfer function is successfully modeled and verified, which shows that the CS amplifier with the heterojunction TFET works as a single-zero and two-pole system. The 3-dB roll-off and unity-gain frequencies are 320 GHz and 2 THz, respectively, which is evidence for circuit applications in the extremely high-frequency regime.