This paper describes the physical properties and sensing characteristics of Yb2O3 sensing membranes grown on Si (100) substrates by reactive sputtering. The structural and morphological features of these films with annealing at various temperatures were studied by X-ray diffraction, X-ray photoelectron spectroscopy, and atomic force microscopy. We found that Yb2O3 films annealed at 800 degrees C exhibit a high sensitivity of 55.5 mV/pH, a low hysteresis voltage of 3.76 mV, and a small drift rate of 1.54 mV/h. The good performance resulting from this annealing condition can be ascribed to the well-crystallized Yb2O3 structure, the thin silica layer, and the large surface roughness. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3089365] All rights reserved.