A novel bistable phenomenon having both a high conductance on state and a high impedance off state has been observed in a forward biased delta‐doped GeSi/Si tunnel diode grown by molecular beam epitaxy. The bistable characteristics are attributed to the different mobile carrier densities in the delta‐doped layers, which leads to the switching of the band structure from a tunnel junctionlike alignment to ap‐i‐njunctionlike alignment or vice‐versa. An on/off conductance ratio larger than 106has been demonstrated for a modified diode structure. The device processing is technologically compatible to the current Si metal‐oxide‐semiconductor technology, making the device useful for a high speed, high density static random access memory cell. ©1995 American Institute of Physics.