In this article, AlGaN/GaN heterostructure ion-sensitive field-effect transistors (ISFETs) were prepared And evaluated by thermal oxidation treatment on the AlGaN surface. The ISFETs were fabricated on the AlGaN/GaN heterostructure and then thermally oxidized with dry oxygen in 600, 700, and 800 degrees C, respectively. It indicates that the performance of the AlGaN/GaN heterostructure ISFETs, such as noise and sensitivity, has been improved owing to the thermal oxidation treatment process at different temperatures. The X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) results indicate that after thermal oxidation treatment at different temperatures, hydroxide who possesses high surface state density wilt transfer to oxide owing to the higher chemical stability of the latter. Moreover, a crystalline alpha-Al2O3 phase, generated at 700 degrees C can not only provide a relatively smooth surface, but also improve the sensitivity to 57.7 mV/pH for the AlGaN/GaN heterostructure ISFETs, which is very close to the Nernstian limit. (C) 2017 Elsevier B.V. All rights reserved.