Provided are: a silicone gel composition providing a silicone gel cured product having excellent heat resistance at high temperatures; and a cured product (silicone gel) thereof. This silicone gel composition is an addition reaction-curable silicone gel composition containing, with respect to the total (mass) of the composition, 1-1,000 ppm of a niobium carboxylate and/or nickel carboxylate represented by the following formula (3).
(R.sup.3COO).sub.fM(3)
(In the formula, R.sup.3 is a homogeneous or heterogeneous monovalent hydrocarbon group, M is at least one metal selected from among nickel and niobium, and f is 2 when M is nickel and 4 or 5 when M is niobium).

Provided is a compound for imparting a thermal plasticity to an organic silicon resin. The compound is a novel vinyl silane compound represented by the following formula (1): ##STR00001##
wherein A independently represents a divalent hydrocarbon group having 1 to 6 carbon atoms; Y independently represents a substituted or unsubstituted monovalent hydrocarbon group having 1 to 12 carbon atoms.

A composition for forming a silica-based insulation layer, a silica-based insulation layer, and a method of manufacturing the silica-based insulation layer, the composition including a solvent; and an organosilane-based condensation polymerization product that includes a structural unit represented by the following Chemical Formula 1: ##STR00001##