Epitaxy by Chemical Vapor Deposition (CVD) is a commonly used technique for the growth of Si alloys in microelectronic devices. In this work, we perform Density Functional Theory (DFT) simulations to study the influence of hydrogenation of Si(001) surfaces on the dissociative adsorption of silane. Silane adsorption is systematically found thermodynamically favorable but its kinetics is limited by H 2 desorption which exhibits an activation energy of 2.4 eV. In addition, our calculations suggest that hydrogenated surfaces tend to reduce the adsorption activation energies compared to uncovered surfaces. This work provides an atomistic description of the SiH 4 adsorption mechanisms and associated energies for the modeling of the epitaxial deposition process using large scale simulation methods.