Various annealing conditions after film deposition have a great effect on electrical and structural properties of low-k films. In this work, we studied hydrogen atmosphere heat treatment effect on low-k films. After the room temperature deposition of a-SiOC:H low-k films following post-deposition-annealing (PDA) for 30 min. at 450°C in an N2 ambient, final annealing was performed for 30 min. at 400°C in an N2, a forming gas 1 (5% H2 + 95% N2), and a forming gas 2 (10% H2 + 90% N2) ambient. The flat band voltage was shifted toward the ideal value of 0.61V after two forming gas anneals, but it increased k values of the films. It was ascribed that hydrogen effectively substitutes defect sites or structural imperfections of low-k films and makes the film more hydrophilic. The FT-IR, XPS analyses and the contact angle measurement supported our conclusion.