In this study, we report a Ho2O3 electrolyte-insulator-semiconductor (EIS) device films deposited on Si substrates through reactive sputtering. The effect of thermal annealing (700, 800, and 900 degrees C) on the structural and surface properties of Ho2O3 sensing film was investigated by X-ray diffraction, X-ray photoelectron spectroscopy, and atomic force microscopy. We found that the EIS device with a Ho2O3 sensing film annealed at 800 degrees C exhibited a higher sensitivity of similar to 57 mV/pH, a lower hysteresis voltage of 2.68 mV, and a smaller drift rate of 2.83 mV h(-1) compared to those at other annealing conditions. This improvement can be attributed to the well-crystallized Ho2O3 structure and the large surface roughness. (C) 2011 Elsevier B.V. All rights reserved.