NOVELTY - 4,8-Dithien-2-ylthieno(2,3-f)(1)benzothiophene based polymers (I) are new.    USE - (I) are useful as donor material in semiconductor composition, and material for photoactive layer of solar cell (all claimed).    ADVANTAGE - (I) have high degree of conjugation and improve carrier mobility.    DETAILED DESCRIPTION - 4,8-Dithien-2-ylthieno(2,3-f)(1)benzothiophene based polymers of formula (I) are new.    m=1-1000;    K1=-R1-M-R1 or -M-;    M=vinylene, ethynylene, monocyclic arylene, bicyclic arylene, polycyclic arylene, monocyclic heteroarylene, bicyclic heteroarylene or polycyclic heteroarylene (all substituted by 3 of aryl, NO2, 1-30C alkyl, 1-30C alkoxy and ethylenedioxy), preferably 2,3-dihydrothieno(3,4-b)(1,4)dioxin-5,7-diyl, 2,1,3-benzothiadiazol-4,7-diyl, naphtho(2,3-c)(1,2,5)thiadiazol-4,9-diyl, (1,2,5)thiadiazolo(3,4-g)quinoxalin-4,9-diyl, 5 lambda (4),11-dithia-4,6,10,12-tetraazatricyclo(7.3.0.0(3,7))dodeca-1(12),2,4,5,7,9-hexaen-2,8-diyl, 2,7-dithia-1,3,6,8-tetraaza-dicyclopenta(a,f)naphthalen-5,10-diyl, (1,2,5)thiadiazolo(3,4-c)pyridin-4,7-diyl, 5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl, 2,1,3-benzoxadiazol-4,7-diyl, 2H-1,2,3-benzotriazol-4,7-diyl moiety of formula (II), 5,6-difluoro-2H-1,2,3-benzotriazol-4,7-diyl moiety of formula (III), 3,4-dinitrothiophen-2,5-diyl, 2-(sulfonyl)thieno(3,4-b)thiophen-4,6-diyl moiety of formula (IV), quinoxalin-5,8-diyl, benzo(g)quinoxalin-5,10-diyl, 2,3-diphenylquinoxalin-5,8-diyl, 2,3-diphenylpyrido(3,4-b)pyrazin-5,8-diyl, 2-benzothiophen-1,3-diyl, thieno(3,4-b)thiophen-4,6-diyl moiety of formula (V), 2-keto-3-fluoro-thieno(3,4-b)thiophen-4,6-diyl moiety of formula (VI), 1,3-thiazol-2,5-diyl, substituted 1,3-thiazol-2,5-diyl moiety of formula (VII), thieno(3,2-b)thiophen-2,5-diyl, (1,3)thiazolo(5,4-d)(1,3)thiazol-2,5-diyl, pyrazin-2,5-diyl, 1,2,4,5-tetrazin-3,6-diyl, 4a,8a-dihydropyrido(3,4-d)pyridazin-5,8-diyl, thieno(3,4-b)pyridin-5,7-diyl, thieno(3,4-b)pyrazin-5,7-diyl, substituted thieno(3,4-b)pyrazin-5,7-diyl moiety of formula (VIII), pyrazino(2,3-b)thieno(3,4-e)pyrazin-6,8-diyl, 2,3-diphenylthieno(3,4-b)pyrazin-5,7-diyl, substituted 4H-thieno(3,4-c)pyrrole-4,6(5H)-dion-1,3-diyl moiety of formula (IX), substituted 3a,7a-dihydro-isoindole-1,3-dion-4,7-diyl of formula (X), substituted 2,5-dihydro-pyrrolo(3,4-c)pyrrole-1,4-dion-3,6-diyl moiety of formula (XI), substituted (E)-1H,1'H-(3,3')biindolylidene-2,2'-dion-6,6'-diyl moiety of formula (XII) or substituted (E)-4H,4'H-(6,6')bi(thieno(3,2-b)pyrrolylidene)-5,5'-dion-2,2'-diyl moiety of formula (XIII);    A1-A3, B1-B3=aryl, heteroaryl, aralkyl (all optionally substituted by less than or equal to 4 Rx), H, 1-30C alkyl, 1-30C alkoxy, CN, NO2, halo, haloalkyl, heteroalkyl, alkenyl or alkynyl, preferably (hetero)aryl moieties of formulae (XIV)-(LII), -CH=CH-R5, -CC-R5 or -CC-Si(CH3)2-R5;    Rx=1-30C alkyl, 1-30C alkoxy, ester, sulfonyl or fluoroalkyl;    R1=substituted thiophene moiety of formula (LIII); and    R2-R6=H, 1-30C alkyl or 1-30C alkoxy.    INDEPENDENT CLAIMS are also included for:    (1) preparing (I); and    (2) semiconductor composition, comprising (I) as donor material and an acceptor material.