The interfacial reactions between Ta‐Ni thin films and (100) GaAs substrate have been analyzed by Auger electron spectroscopy, x‐ray diffraction, and transmission electron microscopy. A pure Ni film reacts with GaAs at 250 °C forming a ternary Ni2 GaAs epitaxial compound, which at 600 °C dissociates to NiGa and NiAs. Ta interacts with GaAs only at 650 °C. In the case of a Ta/Ni film on GaAs at temperatures up to 450 °C only the Ni layer reacts with the substrate forming Ni2GaAs. At higher temperatures the dissociation of Ni2GaAs combined with As outdiffusion results in the structure TaAs/NiGa/GaAs. For the complementary Ni/Ta bilayer, the Ta/GaAs interface is intact up to 500 °C; at this temperature only Ni‐Ta intermixing takes place. At 600 °C, Ni penetrates into the interface with GaAs and forms NiGa. The reaction of the alloy film Ni60Ta40 with GaAs starts at 450 °C by Ni leaching out of the alloy and forming Ni2GaAs at the interface with GaAs. At higher temperatures the reaction results in a structure similar to that obtained for the bilayers with NiGa adjacent to the GaAs substrate. The potential applications of the studied metallization schemes for contacting to GaAs are also discussed.