This study features the fabrication of a planar-form, solid electrolyte modified, (PSEM) Ag/AgCl reference electrode using a screen-printing method. The PSEM Ag/AgCl reference electrode uses agar gel as the inner electrolyte and chloroprene rubber for the liquid junction and insulator. These common low-cost materials and the simple fabrication processes involved render the proposed reference electrode an ideal candidate for cost-efficient mass production. It is shown that the developed reference electrode is insensitive to most of the physiologically important ionic species, including Na+, K+, Li+, Ca2+, NH4+, and Cl-, under continuous measurement conditions. Moreover, as with conventional commercial reference electrodes, the proposed reference electrode exhibits a reversible response, which is maintained until the agar gel dries out. The PSEM Ag/AgCl reference electrode is integrated with an iridium oxide modified Pt-based pH indicator electrode to form a chip-type pH biosensor. The performance of this biosensor is consistent with that obtained from a pH meter based on a macroscopic commercial Ag/AgCl reference electrode. The experimental results confirm that the proposed biosensor is capable of providing precise pH measurements of various real samples. Accordingly, the PSEM Ag/AgCl reference electrode presented in this study provides a viable alternative to the macroscopic Ag/AgCl reference electrode used in many conventional chip-based pH sensors.