A variable capacitance semiconductor structure is disclosed. Embodiments include a capacitor having three plates, a top plate, a middle plate, and a bottom plate. The top plate serves as a positive plate. The middle and bottom plates serve as ground plates for the capacitor. A switching circuit selects between the middle plate and the bottom plate for use as the ground plate of the capacitor. The middle plate is slotted, allowing electric fields to penetrate through the middle plate to the bottom plate. The slots prevent the electric fields from terminating at the middle plate. A different capacitance value can be selected, depending on whether the middle plate or bottom plate is selected as the ground plate. Logic circuitry is configured to control the selection of plates to achieve a variety of capacitance values.