An electrostatic doping approach has been implemented in graphene voltage amplifiers operating in a complementary configuration. The employed controllable electrostatic doping enables the operation of both pFET and nFET at the maximum transconductance point for an optimized voltage gain. In this context, the impact of supply voltage and channel length has been studied in detail. We have identified an unusual scaling trend of the voltage gain as a function of the supply voltage, which is most prominent for shorter channel devices. Our findings also indicate that the voltage gain reported in previous works can be improved threefold by proper pFET/nFET doping, as discussed here.