A method of fabricating a poly crystalline silicon thin film transistor (TFT) is provided. The method includes the operations of forming a poly crystalline silicon having a source, a drain, and a channel region between the source and the drain on a substrate in a predetermined pattern; forming an insulating layer on the poly crystalline silicon; forming a silicon-based heat absorption material layer on the insulating layer; exposing the source and the drain by patterning the insulating layer and the heat absorption material layer and forming a gate and a gate insulating layer corresponding to the channel region; injecting impurities into the source, the drain, and the gate; and heat processing the gate insulating layer and the heat absorption material layer by applying thermal energy to the heat absorption material layer. In the heat treatment, the gate material absorbs some of the heat and passes the remaining heat. The heat treatment of the gate insulating layer under the gate can be performed efficiently.