A thin film transistor includes a gate electrode on a substrate, a gate insulation layer which covers the gate electrode on the substrate, an oxide semiconductor pattern which is disposed on the gate insulation layer and includes a channel portion superimposed over the gate electrode, and low resistance patterns provided at edges of the channel portion, respectively, and including oxygen vacancies, a channel passivation layer on the oxide semiconductor pattern, a reaction layer which covers the oxide semiconductor pattern and the channel passivation layer, and includes a metal oxide, and a source electrode and a drain electrode which contact the oxide semiconductor pattern.