The oxygen-plasma-treated reduced graphene oxide films (RGOFs) are firstly used as the sensing membranes in extended-gate field-effect transistors (EGFETs) for the pH sensors. A large amount of oxygen-containing functional groups are effectively decorated on the RGOFs, resulting in increasing the sensing sites. Furthermore, the reverse pyramid (RP) structure is used as the substrate to increase surface roughness with fixed sensing window. The pH-EGFET current sensitivity of the plasma-treated RGOF on the RP structure can achieve as high as 1.09 uA 1/2 /pH with excellent linearity of 0.999, and a wide sensing range from pH 1 to 13.