Basic THz elements are produced by standard semiconductor science and technology. Therefore, three main material systems are used. These are first of all semiconductors, for active and passive layer formation; metals, for interconnect and contact formation; and insulators, for passivation and isolation purposes. Additionally, these materials are structured in order to produce a device with desired dimensions and characteristics. Semiconductor surfaces, in particular suffer considerable chances during technological processing. Thus, surface and interface issues are essential here to be considered. Semiconductor-dielectric, semiconductor-metal, and semiconductor-semiconductor interfaces as well as surface effects for the case of GaAs are discussed in detail from the point of view of Schottky diodes and heterostructure-based devices for THz applications. (C) 2002 Elsevier Science B.V. All rights reserved.