Thermal emission and capture properties of three dominant electron traps in organometallic vapor phase epitaxial AlxGa1−xAs have been studied by transient capacitance measurements. The traps have activation energies ΔET = 0.82±0.01, 0.62±0.02, and 0.38±0.02 eV, which remain invariant with x. The thermal capture cross section of the traps, however, decreases with increasing x. These results, together with the annealing behavior of the traps, add more evidence to the fact that the 0.82‐eV trap, commonly known as the EL2 center, is related to a Ga vacancy. The 0.82‐ and 0.38‐eV traps exhibit barriers to electron capture ∼0.06–0.08 eV and the concentration of the 0.62‐ and 0.38‐eV traps increases with increasing x.