Abstract: The interfacial SiO2 if layer of Silicon-to-Silicon direct bonding(SDB) has been studied in this paper by means of AES and SEM of interfacial SiO2. It is found experimentally that SiO2 disintegrates into sphere-shaped-like islands with average radius much larger than L, the thickness of the native oxide layer, and of amorphous materials, SiO1.5. The theoretic analysis shows that SiO2 spontaneously disintegrates into islands because the interface free energy will decrease as much as possible.