The focus of this study is to use high resolution synchrotron based photoemission to investigate the initial growth mode of magnesium silicide which has been formed by both stepwise and continuous deposition of metallic Mg onto a thermally grown ultra-thin Si oxide surface. The findings suggest that stepwise deposition of Mg initially results in the growth of Mg silicide islands on the surface. Further magnesium deposition leads to the growth of metallic Mg on the surface of these silicide islands, along with the continued growth of silicide species on the uncovered oxide surface. However, it has been shown that continuous deposition of Mg results in considerably less silicide growth. The thermal stability of Mg silicide and a mechanism for high temperature silicide growth have also been studied using conventional X-ray photoelectron spectroscopy. The results suggest that the presence of oxidised Si acts as a barrier to Si diffusion during vacuum annealing, hence preventing the growth of further Mg silicide. It has also been shown that metallic Mg desorbs from the surface below 300 °C, while Mg silicide is not stable at temperatures above 500 °C in contrast to other metal silicides. © 2010 Elsevier B.V. All rights reserved.