A variable IC capacitor includes a semiconductor layer doped to contain mobile charge carriers. Capacitor electrodes C1 and C2 are disposed adjacent to each other on the layer's surface, gate electrodes G1 and G2 are disposed on opposite sides of C1 and C2, and source and sink electrodes are disposed on opposite sides of G1 and G2. Potentials are applied to the electrodes as needed to inject and then confine a finite charge into the region under C1 and C2. A drive voltage V applied between C1 and C2 causes the charge packet to move back and forth beneath them, such that the effective capacitance C seen by drive voltage V is given by C=Q/V, where Q is the magnitude of the charge packet.