Example embodiments relate to an organic semiconductor polymer, in which fused thiophenes having liquid crystal properties and aromatic compounds having N-type semiconductor properties are alternately included in the main chain of the polymer, an organic active layer, an organic thin film transistor (OTFT), and an electronic device including the same, and methods of preparing the organic semiconductor polymer, and fabricating the organic active layer, the OTFT and the electronic device using the same. This organic semiconductor polymer has improved organic solvent solubility, processability, and thin film properties, and may impart increased charge mobility and decreased off-state leakage current when applied to the channel layer of the organic thin film transistor.