Disclosed herein is a composition containing hetero arylene or arylene showing a p-type semiconductor property in addition to thiophene showing a p-type semiconductor property and thiazole rings showing a n-type semiconductor property at a polymer main chain, an organic semiconductor polymer containing the composition, an organic active layer containing the organic semiconductor polymer, an organic thin film transistor (OTFT) containing the organic active layer, an electronic device containing the OTFT, and a method of preparing the same. The composition of example embodiments, which is used in an organic semiconductor polymer and contains thiazole rings, may exhibit increased solubility to an organic solvent, coplanarity, processability and an improved thin film property.