We reported on the performance and electrical properties of co-sputtering-processed amorphous hafnium-indium-zinc oxide (α-HfIZO) thin film transistors (TFTs). Co-sputtering-processedα-HfIZO thin films have shown an amorphous phase in nature. We could modulate the In, Hf, and Zn components by changing the co-sputtering power. Additionally, the chemical composition ofα-HfIZO had a significant effect on reliability, hysteresis, field-effect mobility (μFE), carrier concentration, and subthreshold swing (S) of the device. Our results indicated that we could successfully and easily fabricateα-HfIZO TFTs with excellent performance by the co-sputtering process. Co-sputtering-processedα-HfIZO TFTs were fabricated with an on/off current ratio of~106, higher mobility, and a subthreshold slope as steep as 0.55 V/dec.