TECHNOLOGY FOCUS - ELECTRONICS - Preferred Device: In the semiconductor device, the density of the porous structure layer (4) formed by silicone resin is 0.7 g/cm3 or less, and 95% by mass or greater of the porous structure layer (4) formed by silicone resin is a silicone resin constituted by silsesquioxane or siloxane, and 20% by mass or greater of the silicone resin is silsesquioxane. The silsesquioxane is methyl silsesquioxane or phenyl silsesquioxane. The substrate (2) is a resin substrate. Alternatively, the semiconductor device (21) comprises: a substrate (22); and a semiconductor element (23); where a porous layer (24) having a density of 0.7 g/cm3 or less formed by a compound obtained by hydrolyzing and condensing at least one type of alkoxysilane selected from monoalkoxysilane, dialkoxysilane, and trialkoxysilane, and tetraalkoxysilane, is provided between the substrate (22) and the semiconductor layer (23). The type of alkoxysilane is a trialkoxysilane, where the trialkoxysilane is methyl trialkoxysilane. Preferred Method: In producing the semiconductor device, the heating is performed by light or by an electron beam. In producing the substrate for the semiconductor element, the percentage by mass of tetraalkoxysilane with respect to all of the alkoxysilanes included in the coating solution is 80% or less. The coating solution containing a surfactant; and the surfactant is removed after heating the alkoxysilanes within the coating film to cause the hydrolysis and the condensation reaction. Alternatively, producing the substrate (31) for the semiconductor element comprises: coating a resin substrate (32) with a coating solution containing an alkoxysilane, to form a first coating film; forming an adhesion layer (33) by heating that causes hydrolysis and condensation of the alkoxysilane within the first coating film; coating the adhesion layer (33) with a coating solution containing an alkoxysilane, to form a second coating film; forming a porous layer (34) having a density of 0.7 g/cm3 or less by heating that causes hydrolysis and condensation of the alkoxysilanes within the second coating film. The coating solution for forming the porous layer (34) including a surfactant; and the surfactant is removed after heating the alkoxysilane within the second coating film to cause the hydrolysis and the condensation reaction. Preferred Substrate: In the substrate, the alkoxysilane which is employed to form the adhesion layer (33) is organo trialkoxysilane; and the alkoxysilane which is employed to form the porous layer (34) is an alkoxysilane selected from tetramethoxysilane, methyltrimethoxysilane, and methyldimethoxysilane.