The deep level electron traps in AP-MOCVD GaAs/undoped AlulcornerGaulcornerAs/n-type GaAs heterostructures have been investigated by means of Deep Level Transient Spectroscopy DLTS). In terms of the experimental procedure, GaAs/undoped AlulcornerGaulcornerAs/n-type GaAs heterostructures were deposited on 2" undoped semi-insulating GaAs wafers by the AP-MOCVD method at $650^{circ}C$ with TMGa, AsH3, TMAl, and SiH4 gases. The n-type GaAs conduction layers were doped with Si to the target concentration of about 2$ imes$10ulcornercmulcorner. The Al content was targeted to x=0.5 and the thicknesses of AlulcornerGaulcornerAs layers were targeted from 0 to 40 nm. In order to investigate the electrical characteristics, an array of Schottky diodes was built on the heterostructures by the lift-off process and Al thermal evaporation. Among the key results of this experiment, the deep level electron traps at 0.742~0.777 eV and 0.359~0.680 eV were observed in the heterostructures; however, only a 0.787 eV level was detected in n-type GaAs samples without the AlulcornerGaulcornerAs overlayer. It may be concluded that the 0.787 eV level is an EL2 level and that the 0.742~0.777 eV levels are related to EL2 and residual oxygen impurities which are usually found in MOCVD GaAs and AlulcornerGaulcornerAs materials grown at $630~660^{circ}C$. The 0.359~0.680 eV levels may be due to the defects related with the al-O complex and residual Si impurities which are also usually known to exist in the MOCVD materials. Particularly, as the Si doping concentration in the n-type GaAs layer increased, the electron trap concentrations in the heterostructure materials and the magnitude of the C-V hysteresis in the Schottky diodes also increased, indicating that all are intimately related.ated.