Disclosed are an organic polymer semiconductor, an ambipolar organic thin film transistor using the same, an electronic device comprising the ambipolar organic thin film transistor and methods of fabricating the same. Example embodiments relate to an organic polymer semiconductor, which may include an aromatic ring derivative having p-type semiconductor properties and a heteroaromatic ring having n-type semiconductor properties in the main chain thereof, and which thus may exhibit both p-type transistor properties and n-type transistor properties when used in the organic active layer of an electronic device, e.g., an organic thin film transistor, an ambipolar organic thin film transistor using such an organic polymer semiconductor, an electronic device comprising the ambipolar organic thin film transistor and methods of fabricating the same.