The dose enhancement factor of X-ray was found in 1970s, because of its bad damage to electronic devices. Purpose: This paper is mainly to calculate the dose-enhancement factor at Au/Si interfaces. Methods: The gradient distribution of dose with X-rays has been studied at and near the interface of Au/Si by Monte-Carlo simulation of particle transportation. The mechanism of dose enhancement is discussed based on the principles of interaction of photon with matter. A 3D Au/Si model has been established by MCNP5 program and the dose-enhancement factors of different thicknesses Au/Si interfaces were calculated by Monte Carlo method. Results: The calculated results demonstrate that there exists a stronger dose-enhancement in the Si side near the interface when the energy of X-ray is 30–300 keV. Conclusions: When the thickness of Au is 0–10 m, dose-enhancement factor ofX-ray increases along with the increase of the thickness of Au, when the thickness of Au exceeds 10 m ,dose-enhancement factor of X-ray decreases along with the increase of the thickness of Au.