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Here, a comparative study of Cr/Au and Ti/Au ohmic contacts on (001) β-Ga₂O₃ was conducted. The electrical behavior from current-voltage measurements and the interfacial composition and microstructure as determined from high-resolution transmission electron microscopy (TEM) with energy dispersive x-ray analysis were compared for the different contacts at selected points in an annealing series (300–700 °C, 1 min. anneals in N₂). Cr/Au contacts became ohmic at temperatures (300–350 °C) approximately 50–100 °C lower than Ti/Au contacts (400–450 °C). Cr/Au and Ti/Au contacts demonstrated optimal ohmic behavior (lowest resistance) when annealed to 450–500 and 500–600 °C, respectively, with Ti/Au contacts yielding amore » lower total resistance than Cr/Au. Cross-sectional TEM images of Cr/Au contacts annealed at 450 °C revealed the presence of Au nanoclusters at the Ga₂O₃ interface and CrO_x layers at both the top of the contact and the Ga₂O₃ interface. Whereas TiO_x also formed at the top and bottom interfaces in 450 °C-annealed Ti/Au contacts, the TiO_x surface layer appeared to be variable in thickness and/or discontinuous, unlike the CrO_x surface layer. Au nanoclusters were not detected at the interface in the Ti/Au contacts. The interdiffusion and oxidation observed in both contact metallizations point to the need for diffusion barriers that may allow these contacts to be used in future Ga₂O₃-based devices that operate at elevated temperatures.« less