Multiple-state　storage　(MSS)　is　common　for　resistive　random　access　memory,　but　the　effects　of　plasma　treatment　on　the　MSS　and　the　switching　properties　have　been　scarcely　investigated.　We　have　demonstrated　a　stable　four-state　storage　capability　of　single　zinc　oxide　nanowire　(ZnO　NW)　treated　by　argon　plasma.　The　electrical　switching　is　attributed　to　the　electron　trapping　and　detrapping　from　the　oxygen　vacancies　(Vos).　The　MSS　relates　to　the　electrical-thermal　induced　distribution　of　the　Vos　which　determines　electron　transport　behavior　to　show　different　resistance　states.　Additionally,　programming　(set　and　reset)　voltages　decrease　with　plasma　treatment　due　to　the　thickness　modulation　of　the　interface　barrier.　©　2015　AIP　Publishing　LLC.