The mechanical properties of Si-doped(111) GaAs crystal for solar cells are investigated by means of a microindentation technique.Vickers microhardness Hv exhibits a nonlinear relationship with the applied load.In th erange of 0.1-1kg,Hv is decreased from 5.59 GPa to 5.03 GPa.Such a phenomenon is explained on the basis of indenter penetration.The Hv value can effectively be presumed by Kicks law, and Meyers index n is calculated to be 1.90.For the fracture toughness Kc of the GaAs crystal, it also displays nonlinear behavior related to the applied load, which is caused by energy dissipation during the development process of cracks on the wafer.