NOVELTY - Polymer (A) comprising one or more diketopyrrolopyrrole repeating units (I) is new.    USE - (A) is useful in semiconductor device, which is an organic photovoltaic device (solar cell), a photodiode, an organic field effect transistor (all claimed) and a thin film transistor device.    ADVANTAGE - (A) has excellent solubility in organic solvents and excellent film-forming properties. (A) provides semiconductor device with high efficiency of energy conversion, excellent field-effect mobility, good on/off current ratios and/or excellent stability.    DETAILED DESCRIPTION - Polymer (A) comprising one or more diketopyrrolopyrrole repeating units of formula (I) is new.    a = 1-3;    a1, b, b1, c, c1, d, d1 = 0-3;    R1, R2 = e.g. H, 1-100C alkyl, 7-100C arylalkyl or carbamoyl;    Ar1, Ar1a = an annulated (aromatic) heterocyclic ring system; and    Ar2, Ar2a, Ar3, Ar3a, Ar4, Ar4a = e.g. Ar1, thiophenyl groups, phenyl group or naphthyl groups.    Full definitions are given in the DEFINITIONS (Full Definitions) Field. INDEPENDENT CLAIMS are included for:    (1) diketopyrrolopyrrole compounds of formulae (III) and (V);    (2) an organic semiconductor material, layer or component, comprising (A) and/or compound (III);    (3) a semiconductor device, comprising (A), compound (III) and/or the organic semiconductor material, layer or component;    (4) preparation of organic semiconductor device, comprising applying a solution and/or dispersion of (A) and/or compound (III) in an organic solvent to a substrate and removing the solvent;    (5) preparation of (III) comprising (a) reacting (in the presence of a strong base) one mole of a disuccinate e.g. dimethyl succinate, with 1 mole of a nitrile compound of formula (R10-(Ar4)d-(Ar3)c-(Ar2)b-(Ar1)a-C?=N) and 1 mole of a nitrile compound of formula (N?=C-(Ar1a)a1-(Ar2a)b1-(Ar3a)c1-(Ar4a)d1-R10a); (b) optionally reacting (III) (where R1 and R2 are H) obtained in step (a) with a halo compound of formula (R1-Hal), in the presence of a base e.g. potassium carbonate, in a solvent e.g. N-methyl-pyrrolidone; (c) optionally reacting (III) obtained in step (b), where R10 and R10a are hydrogen, with a brominating agent e.g. N-bromo-succinimide; and    (6) the preparation of (A).    R10, R10a = H, halo, 1-25C alkyl, 1-25C alkoxy, phenyl group of formula (IVa), thiophenyl group of formula (IVb), benzo(b)thiophenyl group of formula (IVc), naphtho(2,3-b)thiophenyl group of formula (IVd), naphthyl groups of formula (IVe) or (IVf), or anthracenyl groups of formula (IVg)-(IVi); either    R27, R28 = H, 1-25C alkyl or 7-25C aralkyl; or    R27R28 = alkylene or alkenylene which may be both bonded via oxygen and/or sulfur to the thienyl residue and which may both have up to 25 carbon atoms;    R22-R26, R29-R58 = H, halo, 1-25C alkyl (optionally substituted by E and/or interrupted by D), 6-24C aryl (optionally substituted by G), 2-20C heteroaryl (optionally substituted by G), 4-18C cycloalkyl (optionally substituted by G), 2-18C alkenyl, 2-18C alkynyl, 1-18C alkoxy (optionally substituted by E and/or interrupted by D) or 7-25C aralkyl (optionally substituted by G);    X = ZnX12 or -SnR207R208R209; either    R207, R208, R209 = H or 1-6C alkyl; or    two radicals of R207, R208, R209 = common ring and these radicals are optionally branched;    X12 = halo, preferably I or Br, -OS(O)2CF3, -OS(O)2-aryl, preferably p-tolylsulfonyl, -OS(O)2CH3, -B(OH)2, -B(OY1)2, boronate groups of formula (1a) or (2a), BF4Na or -BF4K;    Y1 = 1-10C alkyl;    Y2 = 2-10C alkylene group such as -CY3Y4-CY5Y6-, or -CY7Y8-CY9Y10-CY11Y12-;    Y3-Y12 = H or 1-10C alkyl group, preferably -C(CH3)2C(CH3)2-, -C(CH3)2CH2C(CH3)2- or -CH2C(CH3)2CH2-;    Y13, Y14 = H or 1-10C alkyl; and    Hal = halo, -O-mesylate, or -O-tosylate, preferably Br or I.    With the proviso that (III) excludes 3-benzo(b)thiophen-2-yl-6-(2,3-dihydro-benzo(b)thiophen-2-yl)-2,5-dihydro-pyrrolo(3,4-c)pyrrole-1,4-dione.