Vertical Group III-N devices and their methods of fabrication are described. In an example, a semiconductor structure includes a doped buffer layer above a substrate, and a group III-nitride (III-N) semiconductor material disposed on the doped buffer layer, the group III-N semiconductor material having a sloped sidewall and a planar uppermost surface. A drain region is disposed adjacent to the doped buffer layer. An insulator layer is disposed on the drain region. A polarization charge inducing layer is disposed on and conformal with the group III-N semiconductor material, the polarization charge inducing layer having a first portion disposed on the sloped sidewall of the group III-N semiconductor material and a second portion disposed on the planar uppermost surface of the group III-N semiconductor material. A gate structure is disposed on the first portion of the polarization charge inducing layer.