A compact sensory platform has been fabricated using a graphene field effect transistor (GFET) to identify the biomolecules by pH sensing. The monolayer GFET is driven by an in-built top-gate for detecting the pH of the contacting buffer solution. The GFET device detects the effect of hydroxide ions on a graphite surface. Electrical characteristics of the device were measured after desiccating the buffer solution on the surface of the monolayer graphene. Electrically, the VDirac point shifted toward the positive direction when the pH value of the buffer solution is varied. The transfer curve of the device also moved in the positive direction with increasing pH values, indicating charge transfer from dopant molecules to the surface of graphene. The sensitivity of the device was estimated to be ~48.5 mV/pH. The fabrication of the compact GFET device with an in-built gate provides a platform for effective pH sensing with a user-friendly interface for biosensing applications.