We have developed the deposition and studied the electrical characteristics and thermal reliability of Ru-based contacts on n- type GaN as well as on AlGaN/GaN heterostructure. Amorphous, conducting and transparent RuSiO4 contacts with their extremely low reverse currents and thermal stability up to 900°C, show great potential for use as Schottky contacts to n-type GaN and gate electrodes for AlGaN/GaN HEMT in high temperature, high power applications as well as in UV detectors.