Deep-level transient spectroscopy (DLTS) has been used to characterise the deep levels in InxGa1-xP/In0.20Ga0.80As/GaAs (0.40 less than or equal to x less than or equal to 0.48) pseudomorphic high-electron mobility transistor (pHEMT) grown by solid-source molecular-beam epitaxy (SSMBE). Three different pHEMT devices were investigated, namely; one with single InGaP barrier layer, double InGaP barrier layers and strained InGaP barrier layer. Only one electron trap in the InGaP barrier layer was detected in each of the devices. The activation energy of the electron trap is 0.39 eV for the single-barrier layer device, 0.40 eV for the double-barrier layer device and 0.57 eV for the strained-barrier layer device. The trap concentration is 7.22 x 10(18) cm(-3), 2.38 x 10(20) cm(-3) and 5.02 x 10(20) cm(-3) for these devices, respectively. The current-voltage (I-V) characteristics and transconductance of the devices were measured at 300, 77 and 30 K. The drain saturation current of the devices becomes smaller and the transconductance becomes larger as the temperature decreases from 300 to 30 K. All the devices did not show any collapse in the I-V characteristic or persistent photoconductivity (PPC) at low temperature, suggesting that the trap in the InGaP layer does not have DX centre-like characteristic.