We investigated the thermal stability of ZnO:H films deposited by radio frequency magnetron sputtering at room temperature. The lowest resistivity obtained for a ZnO:H film was 1.99 x 10(-3) Omega-cm with a 10% H-2/Ar flow ratio. The increase in the H-2/Ar flow ratio during deposition plays an important role in producing better thermal stability ZnO:H films as the result of the increase in the percentage of substitutional Ho in the ZnO:H films. The resistivity of the ZnO:H film with 50% H-2/Ar flow ratio can be reduced from 3.49 x 10(-3) Omega-cm to 2.35 x 10(-3) Omega-cm after heat treatment to 300 degrees C. (C) 2011 The Electrochemical Society. [DOI: 10.1149/2.022201esl] All rights reserved.