ABSTRACTWe investigated the electrical properties of the rf-sputtered Hf_xZn_1-xO/ZnO heterostructures. The thermal annealing on ZnO prior to the Hf_xZn_1-xO deposition greatly influences the properties of the heterostructures. A highly conductive interface formed at the interface between Hf_xZn_1-xO and ZnO thin films as the ZnO annealing temperature exceeded 500°C, leading to the apparent decrease of the electrical resistance. The resistance decreased with an increase of either thickness or Hf content of the Hf_xZn_1-xO capping layer. The Hf_0.05Zn_0.95O/ZnO heterostructure with a 200-nm-thick 600°C-annealed ZnO exhibits a carrier mobility of 14.3 cm²V^-1s^-1 and a sheet carrier concentration of 1.93×10¹³ cm^-2; the corresponding values for the bare ZnO thin film are 0.47 cm²V^-1s^-1 and 2.27×10¹² cm^-2, respectively. Rf-sputtered HfZnO/ZnO heterostructures can potentially be used to increase the carrier mobility of thin-film transistors in large-area electronics.