One of the transistors in an integrated circuit fabricated with graphene as the current controlling element, is investigated during its operation, using a chemical tool, XPS. Shifts in the binding energy of C1s are used to map out electrical potential variations, and compute sheet resistance of the graphene layer, as well as the contact resistances between the metal electrodes. Measured shifts depend on lateral positions probed, as well as on polarity and magnitude of the gate-voltage. This non-contact and chemically specific characterization can be pivotal in diagnoses.