Mask heating induced by X-ray exposures from synchrotron or plasma source is of great concern, because it may result in mask distortion due to the thermal stresses generated in the mask. To evaluate the heat transfer and stress issues of lithographic mask structure, numerical simulations were performed by using the MSC/NASTRAN finite element program with IDEAS pre-post processor system on a powerful CONVEX C201 minisupercomputer. For the heat calculations, a microscopic model consisting of a huge number of elements was employed to approach the realistic physical conditions in X-ray lithographic exposure. The temperature distributions, the thermal stress profiles, and the thermal displacement contour of a silicon-tungsten (Si-W) mask structure during X-ray exposure are presented in this paper. The simulated results indicate that the maximum temperatures occur in the regions where the W absorber patterns are most densely populated, and that the thermal stresses usually centralize at the Si-W interface and the edges of W absorber. Considering the absorber pattern displacements, the temperature change of the mask structure should be kept within 3.42°C to suppress the micordistortion to within the acceptable limit of 25 nm for a Si mask substrate with 0.25-μm scale W features.