The present invention relates to the preparation of a polymer comprising a triarylamine function group expressed in chemical formula 1 in the present description, and to a method for preparing an organic thin film transistor using an organic insulation film produced from a semiconductor composition of the polymer and a photopolymerizable composition of the polymer. A polymer compound according to the present invention may be well-mixed with an organic semiconductor material having high crystallinity and may maintain the crystal orientation of the organic semiconductor material at an appropriate level during the formation of a thin film, thus achieving nearly the original high-charge mobility of the organic semiconductor material. Particularly, the organic semiconductor composition prepared using the polymer compound of the present invention as a binder may provide viscosity suitable for each process during spin-coating or printing, thus preparing a thin film transistor having high reliability. Particularly, the characteristics of the transistor may be obtained using a general photocurable thin film as a gate insulation thin film without the use of conventional films comprising fluorine groups such as CYTOP, and therefore the composition and method of the present invention may be easily applied to practical processes.