The present paper describes the evolution of native defects and the introduction of new defects by transient annealing on unimplanted Bridgman (B) or Liquid Phase Epitaxy (LPE) Gallium Arsenide (GaAs). Three techniques covering all the timescales below those available with the conventional furnace annealing were used: Pulsed Electron Beam Annealing (PEBA), Continuous Wave Laser (CWLA) and Rapid Thermal Annealing (RTA). Electronic defects have been investigated by Deep Level Transient Spectroscopy (DLTS). The evolution of native defects and the introduction of new defects, are strongly dependent on the annealing technique. A significant decrease of EL2 concentration has been observed after PEBA, but it is not affected by CWLA or RTA under our annealing conditions. On the contrary, the other native defects EL6 and EL3 are completely annealed by RTA and PEBA. Furthermore, both DLTS spectra recorded after PEBA and RTA on the B substrates show introduction of new defects. However, CWLA does not affect the defects present in B GaAs, but an electron trap termed PL1 was introduced by this treatment in a thin oxide layer formed on the LPE grown GaAs.