The reaction of cobalt with the Si-sacrificial cap in the strained Si/Si1-xGex/Si MBE grown heterostructure was studied. The Si-cap is added to prevent the relaxation of the SiGe and to guarantee uniform and reliable silicidation reaction. The Si1-xGex epilayer, with Ge content between 18 and 28 at%, was highly B doped, while the Si-cap was undoped or B doped either during growth or by ion implantation. Cobalt evaporation was followed by rapid thermal annealing at 450-700°C for 30 sec in N2 or Ar + 10%H2. When the suicide penetrated the Si-cap/Si1-xGex interface, noticeable out-diffusion of Ge and B to the surface was observed. In spite of the presence of the Si-cap significant strain relaxation was observed in three cases: (1) in the implanted samples, although the implantation was confined to the Si-cap, (2) when the Co layer was too thick, such that the suicide penetrated the SiGe layer and (3) when the Ge content in the SiGe layer was relatively high (27.5%).