In a semiconductor memory device and method, phase-change memory cells are
provided, each including a plurality of control transistors formed on
different layers and variable resistance devices formed of a phase-change
material. Each phase-change memory cell includes a plurality of control
transistors formed on different layers, and a variable resistance device
formed of a phase-change material. In one example, the number of the
control transistors is two. The semiconductor memory device includes a
global bit line; a plurality of local bit lines connected to or
disconnected from the global bit line via local bit line selection
circuits which correspond to the local bit lines, respectively; and a
plurality of phase-change memory cell groups storing data while being
connected to the local bit lines, respectively. Each of the phase-change
memory cells of each of the phase-change memory cell groups comprises a
plurality of control transistors formed on different layers, and a
variable resistance device formed of a phase-change material. In
addition, the semiconductor memory device has a hierarchical bit line
structure that uses a global bit line and local bit lines. Accordingly,
it is possible to increase both the integration density of the
semiconductor memory device and the amount of current flowing through
each of the phase-change memory cells.