In this paper, we explore theoretically the possibility of applying AlGaAs/GaAs-based quantum wire systems as a terahertz (THz) ultrasonic generator. For structures such as AlxGa1-xAs/GaAs-based low-dimensional semiconductor systems and semiconductor nanostructures, electrons are confined within the nanometer distance scale so that energies (e.g. electronic subband energy, electron kinetic energy, Fermi energy, etc.) are in the meV scale, which consequently results in the acoustic-phonons generated by heated electrons from these novel systems to be around the THz frequency range. Our theoretical results indicate that: (i) AlxGa-xAs/GaAs-based quantum wires are suitable for generating THz acoustic-phonon signals; (ii) both longitudinal and transverse acoustic-phonon modes contribute to the detected phonon signals; (iii) the THz ultrasound wave can be generated through both intra- and inter-subband scattering processes; and (iv) the strong dependence of the acoustic-phonon emission from a quantum wire on phonon frequency and phonon emission angle can be observed. © 1995 Academic Press.