The electronic properties of the graphene (Gr) Schottky junction with an Al 0.22 Ga 0.78 N/GaN heterostructure on silicon have been investigated, both experimentally and using ab-initio DFT calculations. A peculiar high n-type doping (1.1×10 13 cm-2), observed for Gr in contact with AlGaN, was explained by the combined effect of Fermi level pinning by AlGaN surface states and charge transfer. Spatially uniform current injection across the Gr/AlGaN/GaN heterojunction was revealed by nanoscale resolution conductive atomic force microscopy (CAFM) analyses. Furthermore, a Gr/AlGaN/GaN Schottky diode with excellent rectifying behavior has been demonstrated and used as the key building block for a hot electron transistor (HET) with a 10 nm Al 2 O 3 base-collector barrier. Thanks to the highly efficient hot electron injection from the AlGaN/GaN emitter, this transistor exhibits high on-state current density (J C,ON 1 A/cm 2), high-on state over off-state current density ratio (J C,ON /J C,OFF 10 6) and a common-base current gain 0.15, solely limited by the high Al 2 O 3 base collector barrier. The excellent performances of the Gr/AlGaN/GaN Schottky junction represent an important step towards the development of a HET technology compatible with the state-of-the-art GaN high electron mobility transistors.