A technique using large-area Schottky diode back contacts has been developed to enable high frequency capacitance studies to be carried out on semiconductors without the need to fabricate high quality ohmic back contacts. This technique will find application for very high resistivity materials or for the characterization of novel semiconductors when a method of producing good ohmic contacts has not been established. In this method a back contact much larger in area than the front contact diode under test is used. It is then found that accurate capacitance-voltage measurements can be made of the ionized doping density and, provided the back contact has sufficient leakage, the built-in potential can also be measured. Such specimens may also be used for characterization using the deep level transient spectroscopy (DLTS) technique and this is demonstrated by obtaining DLTS spectra from very high resistivity silicon specimens containing oxygen precipitates and comparing these to similar spectra obtained from more highly doped material. (C) 2003 Elsevier Ltd. All rights reserved.