Abstract: One embodiment of the present invention provides a switching device that can vary a spin-polarized current based on an input signal. The switching device comprises a first conducting region, a second conducting region, and a half-metal region interposed between the first conducting region and the second conducting region. The half-metal region comprises a material which, at the intrinsic Fermi level, has substantially zero available electronic states in a minority spin channel. Changing the voltage of the half-metal region with respect to the first conducting region moves its Fermi level with respect to the electron energy bands of the first conducting region, which changes the number of available electronic states in the majority spin channel, and in doing so, changes the majority-spin polarized current passing through the switching device.