A releasing film (C) comprising a polyester film (A) and a cured silicone resin layer (B) formed on at least one side of the polyester film (A), characterized in that (1) the film (A) is a biaxially oriented film formed of polyethylene-2,6-naphthalenedicarboxylate and has a surface center line average roughness (Ra) of 50 nm or less and (2) the releasing film (C) has a dimensional change of 0.2% or less under a stress of 150 gf/mm2 at 120° C.; and a releasing film (C) comprising a primer layer (D) having a SiO bond, between said film (A) and said cured silicone resin layer (B). The releasing film of the present invention is excellent in heat resistance, surface properties and gas barrier properties, and has small dimensional change rate.