Using thermal oxidation for fabricating iridium oxide (IrOx) electrodes is a good choice for obtaining robust pH electrodes. We fabricated IrOx electrodes at different temperatures for different heating times to obtain electrodes with different E (electrode potential)–pH responses, response rates, and long-term stability. Corresponding characterizations, which include surface morphology, section morphology and composition, surface composition, and surface roughness, are examined intensively. Scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS), and X-ray photoelectron spectroscopy (XPS) are used to carry out the characterizations. All prepared electrodes had a near-Nernstian response, especially when heated at 750, 800, and 870 ℃ for 1.0 and 1.5 h. IrOx electrodes fabricated with these heat treatment parameters had a relatively high response speed, a small potential drift, few cracks on the surface oxide film, thick films, and a small reaction impedance. The surface roughness and composition of the IrOx electrodes fabricated at different temperatures for 1.5 h were also obtained to clarify the relationship between the electrode composition, structure, and properties. Finally, the properties of the electrodes and their relationship with technical preparation parameters and the electrode structure and composition are discussed.