The present invention relates to polymers comprising one or more (repeating) unit(s) of the formula (I), and at least one (repeating) unit(s) which is selected from repeating units of the formula (II), (III) and (IV); and polymers of the formula III, or IV and their use as organic semiconductor in organic devices, especially in organic photovoltaics (solar cells) and photodiodes, or in a device containing a diode and/or an organic field effect transistor. The polymers according to the invention have excellent solubility in organic solvents and excellent film-forming properties. In addition, high efficiency of energy conversion, excellent field-effect mobility, good on/off current ratios and/or excellent stability can be observed, when the polymers according to the invention are used in organic field effect transistors, organic photovoltaics (solar cells) and photodiodes. A-D  (I) B-D  (II) A-E  (III) B-E  (IV)