Power electronics are critical for sustainable energy technologies, but the high cost of semiconductor substrates has made it difficult to reduce cost in $/Ampere and hard to achieve high levels of device integration. For moderate to high voltage applications, wide-bandgap semiconductors are required to ensure high critical breakdown fields. Gallium oxide has been recently proposed as a power device substrate, due its ultra-wide bandgap compared with the current state of the art materials, gallium nitride and silicon carbide. The goal of this project is to characterize electron and hole transport in gallium oxide as a function of the test device structure. By measuring temperature-dependent electrical behavior, we will characterize the charge carrier mobility and density of states functions. By building physics-based models of charge transport, new device structures and performance predictions can be investigated.