Various embodiments of the present disclosure are directed towards a varactor comprising a reduced surface field (RESURF) region. In some embodiments, the varactor includes a drift region, a gate structure, a pair of contact regions, and a RESURF region. The drift region is within a substrate and has a first doping type. The gate structure overlies the drift region. The contact regions are within the substrate and overlie the drift region. Further, the contact regions have the first doping type. The gate structure is laterally sandwiched between the contact regions. The RESURF region is in the substrate, below the drift region, and has a second doping type. The second doping type is opposite the first doping type. The RESURF region aids in depleting the drift region under the gate structure, which decreases the minimum capacitance of the varactor and increases the tuning range of the varactor.