In this research paper, we studied the structural, electronic and thermal properties of the zinc blende ternary alloys (AlGaAs) by the use of first-principles calculations based on FP-LAPW method (Full Potential Linear Augmented Plane Wave) within DFT (Density Functional Theory). Basically, the impact dependence of the lattice constants, band gaps, bulk moduli, heat capacities, Debye temperatures and mixing entropies on the composition x were investigated for different values of x (x = 0, 0.25, 0.5, 0.75, and 1). The computed ground state properties for the parent binary compounds are in reasonable agreement with the available experimental and theoretical results. It is shown that the lattice constant demonstrated a marginal deviation for AlGaAs alloy from Vegard's law. It was observed for the studied alloy that significant deviation of the bulk modulus from LCD (Linear Concentration Dependence). Moreover, it was found that the variation of the energy band gap as function of composition is linear via the mBJ approximation. The thermal parameters of these alloys were investigated by means of the quasi-harmonic Debye model.