Microstructure and chemical composition determine the wetting property of solid surfaces. To achieve hydrophobicity or hydrophilicity, recent efforts have mostly focused on designed patterns and sophisticated surface modification. Here we show the fabrication of a dense amorphous silicon oxynitride (SiON) film by simple annealing of perhydropolysilazane (PHPS), which experiences significant and abrupt transition in surface energy as a function of temperature. The polar component of surface energy, derived from contact angle measurements, exhibits an increase of 20-40 times in an annealing temperature window of ~100 °C, which leads to a 5-fold increase of its total surface energy. On the basis of the chemical analyses, we propose a compositional gradient in the film. Due to this gradient, the hydrophilic SiON film, for instance, can be used as the bond coat material in a double-layer environmental barrier coating system with outstanding oxidation resistant properties.