A lithium niobate (LiNbO3)/silicon (Si) hybrid structure has been developed by the surface-activated bonding of LiNbO3 chips with gold (Au) thin film to Si substrates with patterned Au film. After organic contaminants on the Au surfaces were removed using argon radio-frequency plasma, Au-to-Au bonding was carried out in ambient air. Strong bonding at significantly low temperatures below 100 without generating cracks has been demonstrated.