The techniques based on the measurement of admittance used for characterization of deep levels are reviewed in this paper. Thermal admittance spectroscopy is a technique which allows the measurement of thermal emission rates and thermal activation energies of deep levels in junctions. Optical admittance spectroscopy allows the measurement of optical capture cross sections and optical threshold energies of deep levels in junctions. Thermal admittance spectroscopy can also be applied to III–V alloy junctions in order to characterize the thermal properties of DX centres, which typically appear in these materials. Finally, we show that optical admittance spectroscopy applied to junctions containing DX centres should yield the optical properties of these centres.