The experimental evaluation of stresses at the nanometer scale is a real challenge. We propose an innovative use of High Resolution X-Ray Diffraction to measure local strains induced in silicon by periodic arrays. This technique is non-destructive and allows for the measurement of periodic strain fields in monocrystalline silicon, created in particular by Shallow Trench Isolation process. A 0.58μm-period array of trenches filled with SiO2 gives rise to satellites in reciprocal space maps around the Si substrate peak. The intensity and envelope of these satellites depend on the local strain. The experimental reciprocal space maps are compared to those computed using the kinematical theory from the elastic displacement field calculated with finite element modelling. This technique allows us to study the generation of strain during the main steps of the STI process. During the process, after trenches get filled with oxide and top layers removed, a second diffraction peak appears with a lower intensity than the substrate one. Thanks to finite element modelling, we validate that this peak is caused by an almost constant strain in the silicon active areas. Typical values of strains after trench filling are -1.68*10-3 along × and 1.56*10-3 along z where × and z refer to transverse and perpendicular directions.