In order to fulfill diverse special applications (e.g. food packaging, anticorrosion coatings, flame retardant coatings, biomedical industry and lighter-than air applications), the superior gas barrier property is principal requirement. Based on previous researches, the gas barrier property of membranes could be improved to some extent by changing their component, chemical structure, physical property, fabrication parameters or incorporating impermeable fillers. The above-mentioned approaches provide the enhanced gas barrier property owing to increment in resistance for diffusion of tested gas. That implies the intrinsic factors of the membrane such as free volume fraction of membrane are determined effect on permeability to gas. Accordingly, present work investigated the impact of thermal treatment on enhancement of gas barrier property by manipulating the temperature in the range of 200 °C to 240 °C to adjust the orientation of molecular structure. Based on a series of analysis as well as pure gas measurement, the hydrogen permeability of as-treated membrane decreased by almost 2700 times than that of neat membrane, which is due to the absence of amorphousity. The exceptional gas barrier properties of resultant membrane exhibited great potential for special applications and paved the feasible way for other amorphous precursor to prepare the gas barrier membrane.