NOVELTY - Thermosetting resin composition comprises polysiloxane (I), curing agent and curing catalyst. Cured material formed by heat-processing the thermosetting resin composition has ratio of peak half value width with respect to peak temperature in loss tangent obtained by dynamic-viscoelasticity measurement of 0.18 or less. The polysiloxane has epoxy equivalent of 250-700 g/equivalent.    USE - Thermosetting resin composition is used for semiconductor-device component for semiconductor light-emitting device (all claimed). Uses include but are not limited to photodetector, electro-optical display device, organic semiconductor, organic light-emitting diode, electronic light-emitting display device, organic solar cell apparatus, illuminating device and laser diode.    ADVANTAGE - The thermosetting resin composition has excellent adhesiveness with respect to package for semiconductor light-emitting device, gas-barrier property, heat resistance, light resistance and film formability. The semiconductor light-emitting device is sealed using the resin composition, without producing crack, peeling and coloring even when used for long period of time.    DETAILED DESCRIPTION - Thermosetting resin composition comprises polysiloxane of formula: (R1R2SiO2/2)a(R3SiO3/2)b(SiO4/2)c(O1/2R4)d (I), curing agent and curing catalyst. Cured material formed by heat-processing the thermosetting resin composition, has ratio of peak half value width with respect to peak temperature in loss tangent obtained by dynamic-viscoelasticity measurement of 0.18 or less. The polysiloxane has epoxy equivalent of 250-700 g/equivalent.    R1-R4=1-10C hydrocarbyl optionally containing O or S, or epoxy group-containing hydrocarbyl, where at least one of R1-R4 is epoxy group-containing hydrocarbyl;    a=0.2-1;    b=0.1-0.7;    c=0-0.2;    d=more than 0;and    a+b+c=1.    An INDEPENDENT CLAIM is included for semiconductor-device component, which contains cured material obtained by curing the resin composition.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of the semiconductor light-emitting device is sealed using the resin composition.    Semiconductor light-emitting device (1)    Resin molding (2)    Bonding wire (3)    Fluorescent substance-containing portion (4)    Lead frame (5)