A novel diamond based solid-contact pH-selective microelectrode is reported in the paper for the first time. The diamond films were grown on top of sharp tungsten filaments by HFCVD (Hot Filament Chemical Vapor Deposition). The pH sensitivity of the electrode is achieved via oxygen-termination of the diamond surface with RF oxygen plasma. The MEs were calibrated by zero-current chronopotentiometry registering linearity in the pH 2–12 range. The performance of the diamond microelectrode was demonstrated mapping the pH distribution over corroding Fe-Zn model galvanic cell.