A semiconductor device is provided in which reliability of the semiconductor device is improved by improving an EM characteristic, a TDDB characteristic, and a withstand voltage characteristic of the semiconductor device. An average diameter of first vacancies in a lower insulating layer which configures an interlayer insulating film of a porous low-k film for embedding a wiring therein, is made smaller than an average diameter of second vacancies in an upper insulating layer, and thereby an elastic modulus is increased in the lower insulating layer. Further, a side wall insulating layer which is a dense layer including the first vacancies having an average diameter smaller than the second vacancies is formed on the surface of the interlayer insulating film exposed on a side wall of a wiring trench.