This work reported the physical characteristics and electrical performance of amorphous Al-Zn-Sn-O thin film transistor (a-AZTO TFT) device under the temperature effects of thermal annealing process and various gas plasma post-treatments. The thermal annealing at 450 C could strengthen the oxygen bonding of a-AZTO film, thereby improving the film quality and TFT device performance. In addition, the oxygen deficient can be reduced effectively by the O 2 and N 2 O plasma treatments, respectively, leading to enhanced electrical reliability. Also, the optical energy gap of a-AZTO films with O 2 or N 2 O plasma treatment was measured about 3.5 eV, which indicated that all of the a-AZTO films were insensitive to visible light. On the other hand, the electron mobility of a-AZTO TFT was observed to be promoted after NH 3 plasma post-treatment. The improvement could be attributed to a slight doping effect of H + ions. These results showed the potential of post-treatments for flat panel displays applications of transparent a-AZTO TFT technology.