A study of a new type varactor diode which consists of a semiconductor multilayer structure has been performed. It is shown that such a varactor diode has much stronger nonlinearity in capacitance variation with applied bias voltage than does the conventional varactor due to the two‐dimensional expansion of the depletion region. First, the internal behaviors of this diode are investigated in detail by two‐dimensional computer simulation. Based on the physical insight obtained by the simulation, an approximate analytical expression for the voltage dependence of capacitance is derived for the purpose of practical design. Then, the proposed structure has been experimentally made from Si, whose capacitance‐voltage characteristics are compared with those of the conventional structure made from the same material. Those results substantiate the theoretical predictions.