Photoresponses and microwave characteristics of an area-variable varactor diode are investigated in the frequency range up to 7 GHz. It is demonstrated that the on/off ratio of its capacitance corresponds to 18.5 at 1 GHz. The capacitance is also significantly altered by photoillumination, and a maximum on/off ratio of 450% is achieved at 1 GHz with 1045 nW light power.