Field‐effect deep‐level transient spectroscopy studies have been carried out in molecular‐beam‐epitaxy‐grown GaAs onn+‐GaAs implanted with Si. Four electron traps and one weak hole trap have been detected. Thermal‐emission rate, capture cross section, and activation energy have been found to be influenced by the applied field; the effect was particularly significant in the case of the EL2 level. The energy versus field plots have shown a general tendency that the applied field modulates the activation energy of the trap states; for example, the Arrhenius plot of a single EL2 level at lower fields (<−3 V/cm) is split up into as many as three at higher fields (≳−4 V/cm). These results have been interpreted in terms of recent theories of electron‐phonon interaction on the electron emission from the trap states to the conduction band.