The deep levels have been investigated by the deep level transient spectroscopy (DLTS) technique in Si-and Be-coimplanted undoped semi-insulating LEC GaAs. The four electron traps, Ｅ01（０．２９８），Ｅ02（０．３４１），Ｅ03（０．５５５） and Ｅ04（０．８２１），and two hole traps, Ｈ＇03（０．５４） and Ｈ″03（０．５７）, were observed by majority carrier pulse DLTS measurement. The DLTS signals of the two hole (minority carrier) traps possesses several interesting properties, for example, it is very difficult to make the heights of the DLTS peaks of them reach their maxima by broadening the pulse width, and the heights of the peaks depend strongly on the temperature of the samples. These phenomena can be successfully explained by the theory of the capture and thermal emission of the minority carrier at the trap. It is impossible to measure the energy levels of such two traps using the traditional DLTS technique, therefore, the hole apparent activation energies were measured to be 0.54 and 0.57eV by the constant teuiperature capacitance transient technique, respectively. The Ｈ＇03 and Ｈ″03 are newly observed defects which relate to the Si-and Be-coimplantaion in semi-insulating LEC GaAs.