In a semiconductor having a multilayer wiring structure device on a semiconductor substrate, the multilayer wiring structure includes an interlayer insulating film having at least an organic siloxane insulating film. The organic siloxane insulating film has a relative dielectric constant of 3.1 or less, a hardness of 2.7 GPa or more, and a ratio of carbon atoms to silicon atoms between 0.5 and 1.0, inclusive. Further, the multilayer wiring structure may include an insulating layer having a ratio of carbon atoms to silicon atoms not greater than 0.1, the insulating layer being formed on the top surface of the organic siloxane insulating film as a result of carbon leaving the organic siloxane insulating film.