Interactions of thin Al films with thin films of Ni–Cr alloys and Ni–Cr bilayers deposited on Si are studied using Auger electron spectroscopy and X‐ray diffraction. For Al on the Ni–rich alloy Ni60Cr10 deposited on Si the as‐deposited state is preserved after 30 min annealing at 400 °C apart from some interaction of the inner part of the alloy film with the substrate to form a nickel silicide layer; a heat treatment at 500 °C for 30 min results in a structure of Al3Ni/NiAl0.5Si0.5 + + CrSi2/NiSi/Si. However, for Al on the Cr‐rich alloy Ni20Cr80 deposited on Si under similar conditions Al penetrates to the substrate interface forming a layer consisting of Ni, Si, and Al. The penetration can be prevented by preannealing at 500 °C the Ni20Cr80/Si sample prior to Al deposition — a treatment which results in a structure of CrSi2/NiSi/Si. For the multilayer structures of Al on Cr/Ni bilayer deposited on Si and Al on 500 °C preannealed Cr/Ni bilayer deposited on Si, which yields a structure of CrSi2/NiSi/Si, Al penetration to the substrate is observed after 500 °C anneal. On the other hand a similar heat treatment for Al on Ni/Cr bilayer deposited on Si results in the layered structure of Al3Ni/CrSi2/Si, and even after 30 min annealing at 600 °C no Al is found in the inner part of the CrSi2 layer. Aluminum permeation to the substrate is prevented for the Ni‐rich alloy and for the case of Al/Ni/Cr/Si by the formation of an outer Al3Ni layer which consumes the available Al and acts as a sacrificial barrier. The good stability of Al on preannealed Ni20Cr80/Si is attributed to the presence of O or Ni in the adjacent CrSi2 layer which acts as a diffusion barrier.