A nanoscale investigation on the capacitive behavior of graphene deposited on a SiO2/n+ Si substrate (with SiO2 thickness of 300 or 100 nm) was carried out by scanning capacitance spectroscopy (SCS). A bias Vg composed by an AC signal and a slow DC voltage ramp was applied to the macroscopic n+ Si backgate of the graphene/SiO2/Si capacitor, while a nanoscale contact was obtained on graphene by the atomic force microscope tip. This study revealed that the capacitor effective area (Aeff) responding to the AC bias is much smaller than the geometrical area of the graphene sheet. This area is related to the length scale on which the externally applied potential decays in graphene, that is, the screening length of the graphene 2DEG. The nonstationary charges (electrons/holes) induced by the AC potential spread within this area around the contact. Aeff increases linearly with the bias and in a symmetric way …