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A urea biosensor based on pH-sensitive Sm₂TiO₅ electrolyte–insulator–semiconductor (EIS) has been described. We used X-ray diffraction, Auger electron spectroscopy, and atomic force microscopy to investigate the structural and morphological features of high-k Sm₂TiO₅ sensing membranes that had been subjected to annealing at different temperatures. The EIS device incorporating a high-k Sm₂TiO₅ sensing film that had been annealed at 900°C exhibited good sensing characteristics, including a high sensitivity of 60.5mV/pH (in solutions from pH 2 to 12), a small hysteresis voltage of 2.72mV (in the pH loop 7→4→7→10→7), and a low drift rate of 1.15mVh⁻¹ (in the buffer solution at pH 7). The Sm₂TiO₅ EIS device also showed a high selective response towards H⁺. This improvement can be attributed to the small number of crystal defects and the large surface roughness. In addition, the urea biosensor …