The carrier transport mechanism of low resistance Ti/Al/Au ohmic contact to AlGaN/GaN heterostructures was investigated. Based on a parallel network model consisting of the predominant ohmic path (made by TiN-based contact inclusions) and rest region (no interfacial reaction), the formation of ohmic contact was found to be due to tunnelling of carriers through the thin barrier formed at the TiN-based contact inclusion, where the barrier height was 0.45 eV and the carrier density was 9.0 × 1018 cm− 3.