Contact reactions in the temperature range 250–650 °C between (100) Si and Pd‐W binary alloy films of composition Pd80W20and Pd30W70have been studied by a combination of ion backscattering, x‐ray diffraction, and current‐voltage measurement of Schottky barrier height. For the Pd‐rich alloy, the reaction around 400 °C produced the silicide Pd2Si by depleting Pd from the alloy and resulted in the formation of a two‐layer structure, W/Pd2Si/Si. We have found that the W layer has served effectively as a diffusion barrier for the subsequently deposited Al, indicating that a rectifying contact and its diffusion barrier can be fabricated simultaneously. At higher reaction temperatures, the W layer transforms to WSi2with some mixture of Pd2Si. The alloying of Pd with W has been found to increase the formation temperature of Pd2Si but decrease that of WSi2. In the Pd80W20reaction, Pd2Si forms around 400 °C and WSi2around 500 °C. In the Pd30W70reaction, Pd2Si forms around 500 °C and WSi2around 650 °C.