A GaInP/GaAs/GaInP single quantum well (SQW) sample with unintentionally doped barrier layers was studied using deep level transient spectroscopy (DLTS). A significant DLTS signal was observed, and believed to be from the thermal emission of the well electrons in the quantum well. Furthermore, it was found that only a single major peak was observed, thus indicating that the GaInP/GaAs/GaInP SQW should be at the single-trap level state. Different combinations of V-r (reverse bias) and fill pulse height (FPH) allowed a DLTS study of the region before, within, and beyond the well location. Such an observation, considering the use of an undoped GaInP barrier layer, proves that the DLTS signal is indeed from the well because it is only significant when probed within the well region. The assumption of the DX centers in some previous studies involving the use of AlGaAs barriers can be excluded.