A novel optically modulated high-sensitivity heterostructure varactor, demonstrated as a strong candidate for high-order frequency-multiplier applications, is reported. The device is a delta modulation-doped heterostructure of AlGaAs/GaAs with two Schottky contacts on the top. The capacitance-voltage (C-V) measurements show a C max /C min ratio up to 113 and an extremely high nonlinearity during the transition from high to low capacitance with sensitivity of up to 35. These results are one of the best obtained so far among similar structure devices. In addition, optoelectronic experimental results demonstrate that the slope of the C-V relationship can be modulated by the intensity of the incident optical power. A model describing the source of the reported C-V results is proposed along with the simulation results verifying the observed C-V behavior