The performance of a thermoelectric device fabricated with centimeter-scale monolayer graphene (active size, ∼7 × 1 cm²) was investigated in this study. The carrier type and junction profile of the active graphene layer were modulated by chemical doping. After device optimization, improvements in carrier concentration of at least 200%, which led to enhancements in power factor of at least 600%, were obtained. Under optimal performance conditions, a maximum Seebeck coefficient of ∼350 μV/K and power factor of ∼14000 μW/mK² could be achieved under a temperature difference of 18 K. These thermoelectric parameters are at least three times higher than the best values reported for organic or other graphene-based thermoelectric devices.