The present invention provides a thermal stable low elastic modulus material, which has high thermal stability, is little in change in dynamic characteristics such as coefficient of thermal expansion and elastic modulus within a temperature of −50° C. to 300° C., has an elastic modulus at room temperature of 2-0.01 GPa and is high in reliability of electric insulation regardless of a temperature fluctuation, and provides a semiconductor device using the same. The present invention also provides a thermal stable low elastic modulus resin composition obtained by heat-curing a mixture containing a polyimide, polyamide-imide or polyamide resin or resin precursor, whose cured product has an elastic modulus measured at −50° C. of 2-0.01 GPa, and an oligomer of an organosilicon compound having a functional group capable of causing addition reaction with an NH and/or COOH group.