Abstract: Using a spherical diamond tip of 3 μ_min radius and nano-scratch instrument, the scratch tests were carried out on Si(100) surface under various loads. It was found that with the increase in load, the scratch damage on Si(100) surface would experience the following three stages: formation of surface hillock, generation of hillock and groove, and material removal. While the load varied between 0.5 and 3 mN, the scratch-induced damage was identified as the formation of hillock. As the load increased from 3 to 50 mN, the scratch could lead to the generation of groove. However, the surface hillock kept growing and the hillock still dominated the scratch process. When the normal load attained 50 mN, the depth of the scratched groove increased rapidly and materials removal began to govern the scratch process. Further investigation revealed that the scratch-induced damage of Si(100) could be well characterized based on the analysis of the contact stress between the diamond tip and Si(100) surface. The formation of silicon hillock could be attributed to combination of oxidation and mechanical interaction by scratching under ultra low load