We successfully fabricated the fully transparent Al–Sn–Zn–O thin-film transistors (ATZO TFTs) on glass by RF magnetron sputtering, and then the electrical performances of the ATZO TFTs are optimized with double-channel structures. The double-channel structures are formed by using bilayer ATZO films fabricated successively with different oxygen partial pressure in the sputtering process. The operation mechanism for double-channel structures were clarified. Owing to the double-channel structure, the ATZO TFT demonstrates excellent electrical performances, including a high ON/OFF current ratio (I _on /I _off) of 1.1 × 10⁸, a steep threshold swing SS of 266.3 mV/decade, a superior saturation mobility μ _sat of 134.1 cm²/Vs, and a threshold voltage V _T of 1.2 V.