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A covalent bond is formed when two atoms exchange one or more pairs of electrons. The two atomic nuclei are concurrently drawing these electrons to them. When the difference between the electronegativities of two atoms is too timy for an electron transfer to take place to create ions, a covalent bond is formed.

Ga is trivalent and As is pentavalent, this means there are four electrons per atom in $\mathrm{GaA}s$molecules. The valence charge distribution of the molecule departs from the ideal symmetry, due to which the nature of the bond becomes more covalent.

GaAs is $31\%$ionic and $59\%$covalent because electronegativity of the as atoms causes some partial charge to be imposed on both Gallium and Arsenic atoms despite their covalent bonds. The shared electron pair is drawn to it, resulting in the partial charges on the two atoms.

Thus, the bonding of gallium arsenide is $31\%$ionic and $69\%$covalent as it can be formed by contributing three electrons from gallium and five electrons from arsenic to provide eight electrons needed for four covalent bonds.