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NiAl bi‐ and trilayers are prepared by alternating evaporation of aluminum and nickel on float glass substrates under high vacuum, with individual layer thicknesses between 20 and 100 nm. The samples are subjected to an annealing procedure to temperatures of up to 300 °C in vacuum, and the structural changes induced by the heat treatments are followed by in situ grazing incidence X‐ray absorption spectroscopy experiments at the Ni K‐edge. The results show that the elemental metallic deposits are stable up to 180 °C, while a slow formation of the intermetallic NiAl compound occurs at temperatures above 200 °C. No additional reaction intermediates are detected. Linear combination fits employing spectra of face‐centered metallic Ni and body‐centered NiAl as references allow to quantify the contributions of the respective phases as a function of the temperature and the depth in the multilayer. In general, an increase of the phase fraction of the intermetallic NiAl phase is detected. While the deposited elemental metals cannot completely be transformed into this intermetallic compound for the Al–Ni bilayer system even after prolonged annealing at 240 °C, the analysis of the spectra of the Al–Ni–Al trilayer suggests almost complete conversion to NiAl with body‐centered‐cubic structure. [ABSTRACT FROM AUTHOR]