NOVELTY - A silicon-containing hardenable white resin composition comprises silicon-containing polymer (A), prepolymer (B) obtained by carrying out hydrosilylation reaction of cyclosiloxane-containing ( alpha )-component (II-i) and ( beta )-component chosen from vinyl-cyclohexane compound (III-i), trivinyl-cyclohexane compound (III-ii) and triazinanetrione compound (III-iii), linear siloxane compound (C), component (D) containing organic peroxide and metal catalyst, component (E) containing filler or white pigment, and component (F) containing filler or white pigments.    USE - Silicon-containing hardenable white resin composition is used for hardened material for optical semiconductor package (all claimed), and reflector material for light-emitting diode. Uses include but are not limited to display, vehicle-mounted illumination, signalling lamp, video camera, optical material, recording material, printed circuit board, solar cell, indicator, mobile telephone, etc.    ADVANTAGE - The hardened material obtained using silicon-containing hardenable white resin composition has high light-reflectivity, heat resistance, light resistance and crack resistance, and curvature.    DETAILED DESCRIPTION - A silicon-containing hardenable white resin composition comprises 100 parts mass silicon-containing polymer (A) having weight average molecular weight of 300-100000, 0-200 parts mass prepolymer (B) obtained by carrying out hydrosilylation reaction of cyclosiloxane-containing ( alpha )-component of formula (II-i) and ( beta )-component chosen from vinyl-cyclohexane compound of formula (III-i), trivinyl-cyclohexane compound of formula (III-ii) and triazinanetrione compound of formula (III-iii), and contain 2 or more silicon hydride groups in 1 molecule, 0.1-30 parts mass linear siloxane compound (C) containing carbon-carbon double bond having reactivity with silicon hydride group or methylsilyl group in molecule, component (D) containing 0.0001-10 parts mass organic peroxide and 0-1 part mass metal catalyst, component (E) containing filler having average particle diameter of 3-150 mu m or 0-1500 parts mass white pigment, and component (F) containing filler having average particle diameter of 0.05-3 mu m, or 10-1500 parts mass white pigments (except titanium oxide). The silicon-containing polymer is obtained by hydrolytically condensing organosilane mixture comprising 5-50 mol% organosilane (a) of formula: R1SiX3 (1-1), 0-50 mol% organosilane (b) of formula: R2SiX3 (1-2), 0-40 mol% organosilane (c) of formula: R3R4SiX2 (1-3), 0-40 mol% organosilane (d) of formula: R5SiX3 (1-4), 0-50 mol% organosilane (e) of formula: R6SiX3 (1-5). The sum of organosilane (b) and organosilane (c) in silicon-containing polymer is 5-60 mol%.    R1=2-6C alkenyl, R2=H or 1-6C alkyl;    R3,R4=phenyl optionally substituted by H or 1-6C alkyl, 2-6C alkenyl or 1-6C alkyl, where at least 1 of R2-R4 is methyl;    R5=phenyl optionally substituted by 1-6C alkyl;    R6=2-10C epoxy;    X2,X3=hydroxy, 1-6C alkoxy or halo;    R7-R9=1-6C alkyl or phenyl optionally substituted by 1-6C alkyl;    f=2-10;    g=0-8;    f+g=2 or more;    R10=2-10C alkenyl;    R11,R12=1-10C alkyl, 2-10C alkenyl or 2-10C epoxy group;and    n=1 or 2.    INDEPENDENT CLAIMS are included for the following:    (1) hardened material, which is obtained by hardening silicon-containing hardenable white resin composition; and    (2) optical semiconductor package, has reflector containing hardened material, and having light reflectivity of 80% or more in 460 nm, light reflectivity of 70% or more in 405 nm, and light reflectivity of 60% or more in 460 nm after heat processing for 10 minutes at 300 degrees C.