Bonding of polycrystalline Al to Si(100) and SiO2 (fused silica) was carried out at room temperature by means of surface-activated bonding method. In the present work, different means of surface activation such as irradiation of an argon fast atom beam (FAB) and a hydrogen radical beam (RB) were used. Influence of the exposure to a vacuum atmosphere of the activated surfaces by fast atom irradiation on the bonding behaviour was investigated. The strength of the Al-Si joints sputter cleaned by FAB before bonding reaches as much as 32 MPa. When the activated surfaces were exposed to 30 L (where L is the abbreviation for langmuir (1.33 x 10(-4) Pas)) in the residual gases (mainly vapour), the strength of the Al-Si joint decreased to 20 MPa and approached that of the Al-SiO2 joint. This indicates that the fracture strength of the joint of Al and Si with an intermediate layer of OH groups and oxide is close to that of Al and Si oxide. The adhesion between Al and Si deteriorated strongly because of hydrogen termination on the Si surface which had been irradiated by the hydrogen RB. On the contrary, bonding of Si with native oxides to Al was successful with the hydrogen RB irradiation.