High strength, low temperature fusion bonding of GaAs has been achieved at annealing temperatures between 400 and 420-degrees-C in an ambient H2 atmosphere. The reducing effect of H2 on the oxide interlayer is believed to play an important role. The fracture surface energy of the strongest bonds (0.8 J/m2) is close to that of the bulk material. The tensile fracture strength measured (sigmaf greater-than-or-equal-to 10 MPa) is of the same order as that measured for silicon fusion bonding, hence yielding sufficient strength for most micromechanical devices. Resistivity measurements as well as XTEM analyses indicate the existence of a thin, insulating layer of unrecovered oxide in the bond zone. Also, the anisotropy dependence of the fracture surface energy is theoretically described. The bonding technique could be useful in GaAs-based sensor applications and micromechanical devices, as well as in 3D-integration.