Ge-Sb-Te-based　phase-change　memory　is　one　of　the　most　promising　candidates　to　succeed　the　current　flash　memories.　The　application　of　phase-change　materials　for　data　storage　and　memory　devices　takes　advantage　of　the　fast　phase　transition　(on　the　order　of　nanoseconds)　and　the　large　property　contrasts　(e.　g.,　several　orders　of　magnitude　difference　in　electrical　resistivity)　between　the　amorphous　and　the　crystalline　states.　Despite　the　importance　of　Ge-Sb-Te　alloys　and　the　intense　research　they　have　received,　the　possible　phases　in　the　temperature-pressure　diagram,　as　well　as　the　corresponding　structure-property　correlations,　remain　to　be　systematically　explored.　In　this　study,　by　subjecting　the　amorphous　Ge2Sb2Te5　(a-GST)　to　hydrostatic-like　pressure　(P),　the　thermodynamic　variable　alternative　to　temperature,　we　are　able　to　tune　its　electrical　resistivity　by　several　orders　of　magnitude,　similar　to　the　resistivity　contrast　corresponding　to　the　usually　investigated　amorphous-to-crystalline　(a-GST　to　rock-salt　GST)　transition　used　in　current　phase-change　memories.　In　particular,　the　electrical　resistivity　drops　precipitously　in　the　P　=　0　to　8　GPa　regime.　A　prominent　structural　signature　representing　the　underlying　evolution　in　atomic　arrangements　and　bonding　in　this　pressure　regime,　as　revealed　by　the　ab　initio　molecular　dynamics　simulations,　is　the　reduction　of　low-electron-density　regions,　which　contributes　to　the　narrowing　of　band　gap　and　delocalization　of　trapped　electrons.　At　P　＞　8　GPa,　we　have　observed　major　changes　of　the　average　local　structures　(bond　angle　and　coordination　numbers),　gradually　transforming　the　a-GST　into　a　high-density,　metallic-like　state.　This　high-pressure　glass　is　characterized　by　local　motifs　that　bear　similarities　to　the　body-centered-cubic　GST　(bcc-GST)　it　eventually　crystallizes　into　at　28　GPa,　and　hence　represents　a　bcc-type　polyamorph　of　a-GST.