Disclosed are a composition comprising an organic insulating polymer in which a photo-reactive functional group showing an increased crosslinking degree is introduced into a side-chain, an organic insulating film comprising the composition, an organic thin film transistor (OTFT) comprising the organic insulating film, an electronic device comprising the organic thin film transistor and methods of fabricating the organic insulating film, the organic thin film transistor and the electronic device. The OTFT comprising the organic insulating film of example embodiments may not show any hysteresis during the driving of the OTFT, and therefore, may exhibit a homogeneous property.