A polyorganosiloxane-based composition for film formation which gives a film having low dielectric constant and high modulus of elasticity and useful as an interlayer insulating film in semiconductor devices and the like. The composition for film formation comprises: (A) a product of hydrolysis and condensation obtained by hydrolyzing and condensing, in the presence of an alkali catalyst, at least one member selected from the group consisting of compounds (1) represented by R.sub.a Si (OR.sup.1).sub.4-a (wherein R represents hydrogen, fluorine, or a monovalent organic group; R.sup.1 represents a monovalent organic group; and a Is an integer of 1 or 2), compounds (2) represented by Si(OR.sup.2).sub.4 (wherein R.sup.2 represents a monovalent organic group), and compounds (3) represented by R.sup.3.sub.b (R.sup.4 O).sub.3-b Si--(R.sup.7).sub.d --Si(OR.sup.5).sub.3-c R.sup.6.sub.c [wherein R.sup.3 to R.sup.6 may be the same or different and each represent a monovalent organic group; b and c may be the same or different and each are an integer of 0 to 2; R.sup.7 represents oxygen, phenylene, or a group represented by --(CH.sub.2).sub.n --, wherein n is an integer of 1 to 6; and d is 0 or 1]; and (B) a product of hydrolysis and condensation obtained by hydrolyzing and condensing, in the presence of a metal chelate compound catalyst, at least one member selected from the group consisting of the compounds (1), (2), and (3).