NOVELTY - A sulfonium sulfate compound (I) or (II), is new.    USE - New sulfonium sulfate compound is used for producing layer and column spacers of liquid crystal display panel, and overcoat layer, insulating layer and dielectric layer of color filter, adhesive, sealant, insulating material, coating composition, impregnating composition, laminate, molding material, casting material, substrate for electronic application, printing ink, paint, lacquer, color-proofing material for printing, varnish, potting compound, dipping resin, matrix resin, construction material, lens and solder resist composition (all claimed). Uses include but are not limited to plasma display panel, electroluminescent device, light-emitting diode, charge-coupled device, transistor, very-large-scale integration, magneto-optical disk, solar battery, optical waveguide and automobile topcoat paint.    ADVANTAGE - The heat-curable composition containing sulfonium sulfate compound has excellent hardenability.    DETAILED DESCRIPTION - A sulfonium sulfate compound of formula: R2-S+(R1)-R3.R4-O-S(=O)2-O- (I) or R6-S+(R5)-M-S+(R7)-R8.2/n(Y'(power)(n-)) (II), is new.    Y'(power)(n-)=monovalent or divalent anion of formula: R9-O-S(=O)2-O-, R10-O-S(=O)2-O- or -O-S(=O)2-O-Z-O-S(=O)2-O-;    n=1 or 2;    R1=3-20C cycloalkyl, heterocycloalkyl, group of formula (a), -C(-R33)(R34)-C(R35)=C(R37)-R36, or 1-20C-alkyl;    R2,R3,R5-R8=1-20C-alkyl, 2-20C alkenyl, 2-20C alkynyl, 3-20C cycloalkyl, heterocycloalkyl, 6-20C aryl or heteroaryl;    a,b=0-10;    a+b=1-10;    R4,R9,R10=R2, -NR11R12 or -N=CR13R14;    R11,R12=R2, H, 2-20C alkanoyl, 3-20C alkenoyl or 6-10C aroyl;    R13,R14=1-20C alkyl, 2-20C alkenyl, 2-20C alkynyl, 3-20C cycloalkyl, heterocycloalkyl, 6-20C aryl, heteroaryl, 6-20C aroyl, H, CN, NO2, SR19, OR20, COR21, COOR22 or CONR23R24;    R22=H, 1-20C alkyl, 2-12C alkenyl, 2-20C alkyl optionally substituted by -O-, -S-, -C(O)- or -NRn-, 1-8C alkyl substituted by R22a, -(CH2CH2O)qH, 3-10C cycloalkyl or heteroycloalkyl (both optionally substituted by CO), or phenyl or naphthyl (both optionally substituted by R22c);    R23,R24=H, OR20, 1-20C alkyl, 2-12C alkenyl, 2-20C alkyl substituted by -O-, -S-, -C(O)- or -NRn-, 1-8C alkyl substituted by R23a, -(CH2CH20)sH, -(CH2CH20)t(CO)-(1-8C alkyl), 2-8C alkanoyl, 2-8C haloalkanoyl, 3-6C alkenoyl, benzoyl optionally substituted by F, Cl, Br, I, 1-6C alkyl, -OH or 1-4C alkoxy, 3-10C cycloalkyl, heterocycloalkyl, phenyl or naphthyl;    R25,R26,R33,R34=H, F, Cl, Br, I, CN, NO2, SR19, OR20, COR21, COOR22, CONR23R24, 1-20C alkyl substituted by R25a, -O-, -S-, -C(O)- or -N(Rn)-, 3-20C-cycloalkyl or heterocycloalkyl (both optionally substituted by CO or R25b), 6-20C aryl or heteroaryl (both optionally substituted by R25c);    M=1-20C alkylene, 2-20C alkenylene or 2-20C alkynylene, 3-20C cycloalkylene, heterocycloalkylene, 6-20C arylene or heteroarylene;and    Z=1-20C alkylene optionally substituted by Rzi or Rza, or 6-20C arylene optionally substituted by Rzc.    Full definitions are given in the Definitions (Full Definitions) Section with specified proviso. INDEPENDENT CLAIMS are included for the following:    (1) heat-curable composition, which contains cationic polymerizable compound, and sulfonium sulfate compound (I) or (II); and    (2) method for curing cationic polymerizable composition.