A thin film transistor includes a semiconductor layer including a source region, a drain region, a channel region, first lightly doped drain regions adjacent to the channel region and second lightly doped drain regions adjacent to the first lightly doped drain regions; wherein the second lightly doped drain regions have a doping concentration lower than that of the first lightly doped drain regions. According to the present application, the leakage current in a switching transistor may be further reduced, thereby avoiding instability and even failure in the operation of the assembly caused by overlarge leakage current.