1. A method for changing and sensing data states for a nonvolatile memory cell, the method comprising: switching semiconductor material from a first stable resistivity state to a second stable resistivity state, the second resistivity state lower resistivity than the first resistivity state; switching the semiconductor material from the second stable resistivity state to a third stable resistivity state, the third resistivity state higher resistivity than the second resistivity state; and sensing the third resistivity state as a data state of the memory cell, wherein: the memory cell comprises a portion of a first conductor, a portion of a second conductor, and a switchable memory element comprising the semiconductor material, the semiconductor material is selected from silicon, germanium, or an alloy of silicon and/or germanium, the switchable memory element is disposed between the first and second conductors, the semiconductor material in the first stable resistivity state has a first resistivity when a read voltage is applied to the semiconductor material; the semiconductor material in the second stable resistivity state has a second resistivity when the read voltage is applied to the semiconductor material; the semiconductor material in the third stable resistivity state has a third resistivity when the read voltage is applied to the semiconductor material; the first resistivity, the second resistivity, and the third resistivity are different from each other; the semiconductor material is a doped polycrystalline material that comprises a plurality of grain boundaries; at least some dopant atoms move away from at least some of the plurality of grain boundaries, during switching the semiconductor material from the first stable resistivity state to the second stable resistivity state; and at least some of the dopant atoms move to at least some of the plurality of grain boundaries, during switching the semiconductor material from the second stable resistivity state to the third stable resistivity state.