Integrated pH microelectrodes, which overcome the size limitations of reference electrode and counter electrode, are highly desired for in vivo or in situ microscale measurements. In this work, an innovative integrated solid-state pH microelectrode (ISP) was fabricated using microfabrication technique in combination with electrochemical modification. The as-prepared ISP consisted of a solid-state IrO2 pH microelectrode, an Ag/AgCl reference microelectrode, a gold counter microelectrode, and two spare gold microelectrodes. Its electrochemical performance was characterized by open-circuit potential and cyclic voltammetry. The long-term stability of IrO2 pH microelectrode and the interference of Cl concentrations on the Ag/AgCl reference microelectrode were also evaluated. In addition, the ISP was used to measure the spatial pH distributions within the biofilm on the proton-exchange membrane surface of a microbial fuel cell. The results show that the ISP had high stability, reproducibility and long lifetime, demonstrating a great potential of such a microelectrode for in situ electrochemical measurement of pH distribution at microscale. (C) 2014 Elsevier Ltd. All rights reserved.