This paper describes the structural properties and sensing characteristics of thin Sm2TiO5 sensing membranes deposited on Si substrates by means of a reactive cosputtering method. We used X-ray diffraction, Auger electron spectroscopy, and atomic force microscopy to study the structural and morphological features of these films after they had been subjected to annealing at various temperatures. The electrolyte-insulator-semiconductor (EIS) device with a Sm2TiO5 sensing film that had been annealed at 900 degrees C exhibited a higher sensitivity (0.5 mV/pH in solutions from pH 2 to 12), a smaller hysteresis voltage (2.72 mV in the pH loop 7 -> 4 -> 7 -> 10 -> 7), and a lower drift rate (1.15 mV/h in the buffer solution at pH 7) than those prepared at other annealing temperatures. The Sm2TiO5 EIS device also showed a high selective response toward H+. This improvement can be attributed to the small number of crystal defects and the large surface roughness. Besides, the enzymatic EIS-based urea biosensor fabricating a Sm2TiO5 sensing membrane annealed at 900 degrees C allowed the potentiometric analysis of urea with a sensitivity of 17.78 mV/mM. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3439676] All rights reserved.