This study first investigated the thermal stability of Ni(Ta) silicides on ultra-thin silicon-on-insulator (SOI) substrates. The presence of Ta atoms significantly decreased the resistivity of Ni(Ta)Si thin films. Compared to the Ni/Si system, the Ni(Ta)Si films formed on ultra-thin SOI were found to exhibit remarkably improved morphological stability. For the Ni(Ta)/SOI samples, the process window of low-resistivity Ni(Ta)Si silicides was extended to high temperature up to 850 °C. This study explained these phenomena in terms of the thermally robust Ni(Ta)Si/SiO 2 interface and Ta-accumulated grain boundaries in the Ni(Ta)Si films. Ta-accumulated grain boundaries may act as adhesive in Ni(Ta)Si films, effectively hindering the agglomeration of Ni(Ta)Si films and thus extending the low-resistivity process window of Ni(Ta)Si silicides. This work demonstrated the potential of Ni(Ta) silicidation on ultra-thin SOI substrates for device applications.