We have obtained the three independent complex components P 11 (ω), P 12 (ω), and P 44 (ω) of the linear piezo-optical tensor P ijkl (ω) [Δe ij (ω)=P ijkl (ω)X kl ] of GaAs inthe ∼1.5-5.4-eV photon-energy range (visible UV) by applying static uniaxial stress (X) along the high-symmetry directions [100] and [111] and manuring the stress-induced changes in the dielectric function e(ω). These measurements were performed using a conventional rotating analyzer ellipsometer at room temperature