Hydrogenated amorphous silicon thin film transistor with inverted staggered structure is fabricated using a novel chemical treatment process for growing gate aluminum oxide. The Al gate is treated by Na2CO3 + Na2CrO4 + Na2SiO3 water solution at 60 degrees C and annealed at 400 degrees C in the O-2 environment before the deposition of thin film transistor by plasma-enhanced chemical vapor deposition. The off-current of the transistor is in the picoampere range and on-off current ratio exceeds 5 x 10(6). The highest field effect mobility achieved in the linear region is 0.28 cm(2)N-s and the subthreshold swing is 1.1 V/decade.