A varactor device includes a support structure, an electrically conductive layer at the backside of the support structure, two semiconductor structures including doped semiconductor materials, two contact structures, and a semiconductor region. Each contract structure is electrically conductive and is connected to a different one of the semiconductor structures A contract structure couples the corresponding semiconductor structure to the electrically conductive layer. The semiconductor region is between the two semiconductor structures and can be connected to the two semiconductor structures. The semiconductor region may include non-planar semiconductor structures coupled with a gate. The gate may be coupled to another electrically conductive layer at the frontside of the support structure. The varactor device may further include a pair of additional semiconductor regions that are electrically insulated from each other. The additional semiconductor regions may be coupled to two oppositely polarized gates, respectively.