With growing interest in applications in the THz regime, techniques related to THz-devices and circuits become increasingly important, In the frequency range of the so-called submillimeter waves, device dimensions are comparable to the wavelength. Therefore, hybrid techniques with non-reproducible parasitics are not suitable for THz-circuitry, Recently, many efforts have been made on the integration of several devices and of devices with other circuit elements like filters and antennas. Monolithic integration enables realisation of large-area arrays for quasi-optical power combining and THz imaging. In this paper, a brief description of the technologies on THz-devices using III-V semiconductors is presented. These include Schottky-barrier diodes, heterojunction barrier varactors (HBV's), and a new device concept using rf-swing-controlled charge transport for THz frequency multipliers, Furthermore, an account of the key technological developments required for THz integration is given.