Amorphous　oxide　semiconductor　(AOS)　field-effect　phototransistors　(FEPTs)　are　promising　candidates　for　emerging　photodetectors.　Unfortunately,　traditional　lateral　AOS　FEPTs　suffer　from　low　photosensitivity,　slow　response　time　and　inadequate　mechanical　flexibility,　which　restrict　their　widespread　commercial　application.　In　this　work,　novel　AOS-based　vertical　field-effect　phototransistor　(VFEPT)　arrays　are　presented,　where　the　semiconducting　layer　and　source　and　drain　electrodes　are　deposited　by　inkjet　printing.　Benefitted　from　the　unique　vertical　structure　and　ultrashort　channel　length,　the　exciton　dissociation,　carrier　transfer,　and　collection　efficiency　were　dramatically　enhanced,　resulting　in　excellent　photoelectric　performance　in　VFEPT　devices,　which　was　better　than　that　of　the　traditional　lateral　AOS　phototransistors.　Moreover,　flexible　AOS　VFEPT　arrays　were　investigated　for　the　first　time　on　polyimide　substrates.　Due　to　the　unique　vertical　architecture,　the　carrier　transport　was　negligibly　affected　by　the　strain-induced　in-plane　cracks　of　the　semiconductor　channel　layer　during　the　mechanical　bending　process,　which　overcame　the　maximum　bending　limit　of　traditional　lateral　AOS　thin-film　transistors　to　ensure　a　transistor　technique　that　gives　notable　mechanical　robustness　against　repeated　mechanical　bending.　Hence,　this　work　provided　a　new　pathway　in　emerging　applications　for　AOS　photodetectors　with　sensitivity,　transparency,　and　flexibility.　Copyright　©　2018　American　Chemical　Society.