Soft switching, spin-valve Co/Cu heterostructures have been electrodeposited onto n-type (100) GaAs. A symmetric spin-valve configuration is used which incorporates an artificially hard substructure. A magnetoresistance change of up to 5.4% is observed with sensitivities up to 0.55% per Oersted and a saturation field of 100 Oe, the highest sensitivity so far observed in electrodeposited structures. The magnetoresistance measurements show a double switching step which we conclude is due to the free layers having differing coercivities. The Co/GaAs interface induces an in-plane anisotropy in the films which is responsible for these remarkable spin-valve properties. (C) 1999 American Institute of Physics. [S0003-6951(99)00915-8].