Magnetic and transport properties of a hard-soft spin valve structures have been investigated. A first series of sandwiches composed of an artificial antiferromagnetic (AAF) Co/Ru/Co sandwich decoupled from a soft Fe/Co buffer layer as follows: Fe-50 (Angstrom)/Co-5 Angstrom /Cu-30 (Angstrom)/Co-30 (Angstrom)/Ru-5 Angstrom /Co-30 (Angstrom)/Cu-20 (Angstrom)/Cr-20 (Angstrom) has been prepared. This sandwich presents a giant magnetoresistance (GMR) of 1.7% and an exchange coupling strength of approximately - 1.73 erg/cm(2). Afterwards, we have grown a second series of sandwiches in which the Cu/Cr capping layer has been replaced by a 15-Angstrom thin semiconductor layer of ZnS, covered by a soft ferromagnetic layer of Co-5 (Angstrom)/Fe-50 (Angstrom). Surprisingly, the giant magnetoresistance for the last sandwiches has been increased by a factor of 2, up to 4%. To explain this non-expected result, we have performed atomic force microscope imaging at the semiconductor layer surface. The results show that the semiconductor layer is not homogeneous and contains a non-negligible density of gin-holes, that are responsible of a direct magnetic coupling between the upper 30 Angstrom Co layer of the AAF and the Co 5 Angstrom /Fe 50 Angstrom bilayer. This coupling induces a strong asymmetry between the magnetic layers of the AAF and consequently an enhancement of the GMR.