An organic semiconductor material, layer or component, comprising a copolymer of the formula wherein v and w each generally are from the range 4 to 1000; A is a benzodithiophene repeating unit of the formula II or III and COM is selected from certain arylene-type repeating units, and combinations thereof. The present copolymers, as well as composites thereof, may be used as semiconductor in the preparation of electronic devices such as photodiodes, organic field effect transistors and especially organic photovoltaic devices such as solar cells.