It was found that strong bonding takes place when a pair of clean, mirror‐polished silicon surfaces are contacted at room temperature after hydrophilic surface formation. Bonding strength reaches the fracture strength of silicon bulk after heating above 1000 °C. Electric resistivity at the interface is less than 10−6&OHgr;/cm2. Bondingp‐type silicon ton‐type silicon forms a diode. The reaction between silanol groups formed on the surface may cause the bonding force. Heating above 1000 °C was thought to diffuse oxygen to inside the silicon bulk, forming an epitaxial‐like lattice continuity at the interface.