We have applied high resolution synchrotron X-ray diffraction to two-dimensional (2D) Si gratings with wavelengths of 300 and 400nm. We show that this method is very sensitive to both the geometry (grating wavelength, height, and angle of inclined sidewall) and the state of strain. Morphology changes produced by vacuum annealing can be detected so that the mass transport rates on Si surfaces can be measured. Strain measurements show that grating pillars covered with 1 lnm of thermal oxide were under tension (ε = 3.7 × 10−4). This strain was elastically relaxed by removing the oxide.