Low temperature (LT) GaAs grown on semi-insulating GaAs by molecular beam epitaxy has been investigated by field effect deep level transient spectroscopy at several reverse bias fields ranging from -1x10(5) to -4x10(5) V/cm. The activation energy, capture cross section, and electron-phonon coupling parameter all have been found to be modulated by the applied field. The theories of the Schottky effect and the electron-phonon coupling effect have been considered to interpret the electron conduction mechanisms in LT GaAs.