Strength and fracture toughness of (100) oriented GaAs wafers are analyzed by fracture and indentation testing. Using finite element method (FEM) critical fracture stresses are calculated from the fracture loads of wafers tested under biaxial bending, whereas atomic force (AFM), scanning electron microscopy (SEM) and acoustic C-scan microscopy of deformation and cracking patterns around micro- and nano-indentations provided information on yielding, crack initiation and crack growth resistance. Through fracture mechanical evaluation of these results critical defect sizes are derived, which are tolerable without strength degradation. It is shown, that a fracture strength of at least 800MPa can be achieved by careful fabrication even of 6' wafers. This figure is much higher then the prescribed minimum strength level estimated to avoid premature failures during wafer handling and processing routes.