Enhancement-mode amorphous indium gallium zinc oxide (α-IGZO) channel thin film transistors (TFTs) with a 6 μm gate length and a 100 μm gate width were fabricated on glass substrates by rf magnetron sputtering near room temperature. The resistivities of the α-IGZO films were controlled from 10-1 to 103 Ω cm by varying the deposition power of 75–300 W. The n-type carrier concentration in the channel was 6.5×1017 cm-3. The gate oxide was 90-nm-thick SiNx, deposited by plasma enhanced chemical vapor deposition at 70 °C. The bottom-gate TFTs had saturation mobility of ∼17 cm2 V-1 s-1 and the drain current on-to-off ratio of ∼≫105, a subthreshold gate-voltage swing of ∼0.5 V decade-1, and a threshold voltage of 2.1 V. In the TFT with a gate length of 6 μm and a gate width of 100 μm, the relative change of saturation mobility and threshold voltage was less than ±1.5% after 500 h aging time at room temperature. This demonstrates that α-IGZO film- - s are promising semiconductor materials for long-term-stable transparent TFT applications.