A method for manufacturing a thin film transistor includes forming a light shielding layer and a buffer layer covering the light shielding layer on a substrate. The method includes forming an active layer including a peripheral region and a channel region. The method includes forming a gate insulating layer covering the channel region and forming a contact hole exposing the light shielding layer. The method includes forming a source region and a drain region disposed on both sides of the channel region. The method includes forming an electrode layer including a gate electrode, a source electrode and a drain electrode spaced apart one another. The method includes forming a dielectric layer covering the gate electrode, the source electrode, the drain electrode and the buffer layer.