Highly　sensitive　photodetection　is　indispensable　in　applications,　such　as　remote　sensing,　imaging,　and　smoke　alarming.　III-V　nitrides　are　promising　candidates　for　photodetectors　due　to　their　continuously　tunable　bandgap,　radiation　hardness,　and　temperature　stability.　However,　the　sensitivity　of　traditional　III-V　nitride-based　photodetectors　is　limited　by　poor　crystal　quality　which　stems　from　lattice　mismatch-induced　point　defects　and　dislocations.　Recently,　a　new　type　of　graphene-colloidal　quantum　dot　(QD)　hybrid　phototransistor　has　been　preferentially　used　to　obtain　high　detection　sensitivity,　but　III-V　nitride-based　colloidal　QDs　are　hard　to　synthesize.　Here,　a　highly　sensitive　QD/graphene　hybrid　photodetector　is　demonstrated　by　using　self-assembled　InGaN　QDs.　The　photoconductance　in　the　2D　graphene　sheet　is　tuned　by　photogenerated　carriers　in　the　quantum　dots　when　illuminated,　and　this　effect　leads　to　a　current　gain　mechanism.　The　photodetector　achieves　an　ultrahigh　responsivity　over　10(9)　A　W-1,　a　current　gain　of　10(9)　and　fW　light　detectivity　even　at　room　temperature.　This　study　paves　the　way　for　new　types　of　highly　sensitive　III-V　nitride-based　photodetectors　despite　the　insufficient　crystal　quality.