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 switchable memory element disposed between the first and second conductors.