. . . . "A method of forming an interlayer insulating film, wherein a material containing, as a main component, an organic silicon compound represented by the following general formula: R1 x SiH4-x (where R1 is a phenyl group or a vinyl group; and x is an integer of 1 to 3) is caused to undergo plasma polymerization by means of plasma chemical vapor deposition to form an interlayer insulating film which is" .