The velocity-field characteristics of hot electrons in planar organometallic vapor phase epitaxial (VPE) AlxGa1-xAs (0.1 ≤ x ≤ 0.6) transferred-electron devices have been measured by the probe technique. The characteristics in layers with x ≤ 0.30 show normal subthreshold behavior. For x > 0.30, the characteristics exhibit high values of drift velocity. The effects are more enhanced when an undoped 0.4-µm GaAs buffer layer is grown first on the GaAs: Cr substrate before the ternary layer is grown. Monotonically increasing drift velocities with electric field, with a value of 2 × 107cm/s at 6 kV/cm, have been measured in these devices. These effects and overshoots in the pulsed current-time profiles indicate the onset of real-space electron transfer at the heterointerface at high fields.