III-V bonding, while showing great promise in the development of world-record solar cell performance, has not been used widely in other applications. A better understanding of the fundamental nature of bonded interfaces leads to insight about the bonding process and a more thorough investigation for other device applications. We addressed the electrical conductivity across various III-V wafer bonded pairs based on understanding the nature of the grain boundary that exists at the interface. The combinations included different materials, different miscut (tilt), and in-plane (twist) misorientation. With results from bonding of several different materials combinations, surface orientations, and passivation treatments, as well as an assessment of barrier heights reported in the literature for transport in polycrystalline III-V materials and other III-V bonded materials combinations, a general model has emerged which suggests that direct wafer bonding of III-V and other materials has a wide variety of applications. The electrical characteristics of a grain boundary, whether in polycrystalline material or at a bonded interface, are determined by the presence of defect states and interfacial charge which create band bending and Fermi level pinning. The barrier heights and widths from zero bias conductance vs bias measurements over a wide range of temperatures and for different materials were compared to the band structure simulations of bonded semiconductor heterojunctions with resultant I-V curves showing good agreement between experiment and theory. The role of sulfur to passivate the interface corresponded to a drop in the interface state density by a factor of three. Based on this study which combines experimental results and transport modelling, it is expected certain material combinations and orientations exhibit higher electrical conductivity across the interface, but more importantly, modelling supports the finding that high doping at mismatched interfaces helps to significantly reduce the interface barrier height.