Zinc oxide thin films prepared by sol-gel and doped with different aluminum percentages were deposited by spray-pyrolysis deposition techniques on FTO and ITO substrates. The films were applied as the sensitive layer of pH-sensors EGFET devices. ZnO:Al films on FTO substrates shows a decrease in sensor quality with the dopant percentage increase. The opposite occurs when the substrate was ITO. The best quality film to be used as pH-sensor on FTO substrates was the ZnO:Al (3%) with 29 mV/pH sensitivity value and linear adjust of 0.99. For ITO substrates the best quality was achieved for ZnO:Al (10%), with sensitivity about 30 mV/pH and 0.99 linear adjust.