An investigation on the current conduction mechanisms of AlGaN/GaN Schottky contacts is presented in this paper. The ideality factor and the barrier height of Schottky contact on AlGaN/GaN heterostructure are calculated by I-V measurement in a wide temperature range. By subtraction of generation-recombination, tunneling and leakage currents from the total current, the “pure" Schottky barrier height can be evaluated with higher physical relevance. After analyzing the variational rules of Schottky contact characteristics on AlGaN/GaN heterostructure at 300—550K, it is concluded that surface leakage current plays an insignificant role in producing the gate leakage current of AlGaN/GaN HEMT.