The mechanical strength of silicon wafers of 100 μm thickness was studied. Loading of the wafers was carried out by the "ring-on ring" method, stress and deflection under the small ring were determined by finite element modeling. The validity of the calculation model was checked by comparing the dependences of the deflection under the small ring on the load obtained in the experiment and by the simulation. The effect of methods of wafers obtaining and their surface treatment on the strength, as well as the connection between the strength and surface roughness characteristics were shown. Keywords: silicon, strength, chemical polishing treatment, surface roughness.