Capacitance–voltage and capacitance–frequency characteristics of the metal/n-GaN/metal Schottky contacts with Au, Al and Ag electrodes were investigated as a function of the temperature and external electric field in the frequency range from 100 to 300kHz. Forward capacitance–voltage measurements were carried out in the frequency range from 100Hz to 20MHz. The temperature capacitance coefficient and the electrical tunability were measured as a function of the external DC field for all contacts. The capacitance and dielectric loss measurements show relaxation peaks from 4 to 11kHz for some electrodes, indicating that interfacial effects play an important role in the electrical properties of the GaN Schottky barrier contact. Low-frequency relaxation studies were conveniently used to probe interfacial characteristics of the contacts.