(1 1 0)-oriented diamond films were grown by microwave plasma chemical vapor deposition technique, followed by an optimized hydrogen-plasma treatment process. Thermal stability of hydrogenated diamond films were studied by annealing in nitrogen atmosphere at temperature varied from 400 to 950 degrees C. Reflection electron energy spectroscopy associated with X-ray photoelectron spectroscopy indicates that approximate at. 50% hydrogen was present at the surface of hydrogenated diamond films, which is close to the theoretical value. Pinning effect in surface Fermi level in hydrogenated diamond films could not be eliminated by annealing in nitrogen until the temperature was exceeded 950 degrees C. The films underwent hydrogen desorption and subsequent graphitization mainly on the very surface region without significant bulk modification. Besides, hydrogenated diamond films annealed in N-2 at 950 degrees C showed similar hydrophilicity and resistance to that of the oxidized one, indicating rupture of C-H bond on the surface of hydrogenated diamond films. (C) 2015 Elsevier B.V. All rights reserved.