Deep level defects in undoped semi-insulating GaAs are investigated by photo-luminescence (PL) technique. Several PL emissions related to deep level defects and their behaviors have been observed. The emission band at 0.69eV is due to the well known main mid-gap level EL2 and the 0.77eV PL bands attributable to the transition from the con-duction band to the As_(Ga)donor level. It is suggested that the 1.447eV and 1.32eV PL emis-sions are caused by the double acceptors Ga_(As), with levels 78meV and 203meV above the valence band, respectively.