In the present study molecular dynamics simulations were carried out to investigate the deformation of pure FCC aluminum and diamond cubic silicon interfaces under shear stress. A second nearest-neighbor modified embedded atom method was used to describe the interactions between Al-Al, Si-Si and Al-Si atoms. The critical shear stress (CSS) was determined for various Al/Si and Al/Al interfaces with different alignments and orientations. Structural analyses show that the deformation is localized at approximately 10 Å thickness of the interface in Al. The critical shear stress of Al/Si interface was found to be significantly lower than the critical tensile stress due to the partial stick-slip in sliding. In addition, it has been proven that there is no explicit relationship between shear and tensile critical stresses, which is fundamentally different from isotropic materials, where the shear stress is about half of the tensile stress. The misorientation has a dramatic effect in reducing shear stress at Al/Al interfaces, but has no effect on CSS in Al/Si. As a result, it was shown that introducing Si improves the strength of the interface (and the composite material in general) for different grain orientations.