Doping and stability of monolayer low defect content graphene transferred on a silicon dioxide substrate on silicon are investigated by micro-Raman spectroscopy and atomic force microscopy (AFM) during thermal treatments in oxygen and vacuum controlled atmosphere. The exposure to molecular oxygen induces graphene changes as evidenced by a blue-shift of the G and 2D Raman bands, together with the decrease of I 2D/I G intensity ratio, which are consistent with a high p-type doping (∼1013 cm–2) of graphene. The successive thermal treatment in vacuum does not affect the induced doping showing this latter stability. By investigating the temperature range 140–350 °C and the process time evolution, the thermal properties of this doping procedure are characterized, and an activation energy of ∼56 meV is estimated. These results are interpreted on the basis of molecular oxygen induced ∼1013 cm–2 p-type doping of graphene with stability energy >49 meV and postdoping reactivity in ambient atmosphere due to reaction of air molecules with oxygen trapped between graphene and substrate.