NOVELTY - An organosilicon compound is new.    USE - Organosilicon compound for thermosetting composition (claimed) used as LED composition for integrated circuit (IC) package, sealing material of semiconductor, sealing material of optical semiconductor, insulating film, sealing material, optical lens, optical film, optical sheet, adhesive agent, electronic material, insulating material, interlayer insulation film, coating material, ink, coating material, molding material, potting material, liquid crystal sealing material, sealing material for display devices, solar cell sealing material, resist material, color filter, electronic paper material, hologram material, solar cell material, fuel cell material, display material, recording material, waterproof packaging, dampproofing material, battery solid electrolyte, gas separation membrane and contact lens.    ADVANTAGE - The organosilicon compound is excellent in quality, such as stability.    DETAILED DESCRIPTION - An organosilicon compound of formula (1) is new.    R1-R11=H, 2-20C alkenyl in which H may be substituted with F and -CH2- may be substituted by -O- or cycloalkylene or 1-20C alkyl in which H may be substituted with F and -CH2- may be substituted by cycloalkylene; and    R12,R13=H, 1-45C alkyl in which H may be substituted with F and -CH2- may be substituted by -O-, -CO-, -CH=CH-, cycloalkylene or cycloalkenylene, optionally substituted aryl or arylalkyl comprised by 1-45C alkylene in which H may be substituted with F and -CH2- may be substituted by -O-, -CH=CH- or cycloalkylene; and    n=0-4.    An INDEPENDENT CLAIM is included for a manufacturing method of organosilicon compound (1) involving reacting organosilicon compound of formula (2) or organosilicon compound of formula (5) and organosilicon compound of formula X-Si(R9)2-O-Si(R9)2-O-Si(R9)2-O-Si(R11)2-R12 (3) with n times mole in which n is 0-4, and reacting organosilicon compound of formula X-Si(R10)2-R13 (4) with (4-n) times mole.    X=halo; and    M=monovalent alkali metal.