The invention relates to a process of preparing regioregular polymers, in particular head-to-tail (HT) poly-(3-substituted) thiophenes or selenophenes with high regioregularity and defined molecular weight, to novel polymers prepared by this process, to the use of the novel polymers as semiconductors or charge transport materials in optical, electrooptical or electronic devices including field effect transistors (FETs), electroluminescent, photovoltaic and sensor devices, and to FETs and other semiconducting components or materials comprising the novel polymers.