The temperature-dependent DC characteristics and noise performance of In0.49Ga0.51P/In0.15Ga0.85As/GaAs low noise pseudomorphic high electron mobility transistors (PHEMTs) with the gate dimensions of 0.25x160 mum(2) are investigated at 12 GHz with temperature ranging from 300 to 450 K. It is found that the variation of the turn-on voltage for drain-to-gate Schottky diode is -1.05 mV/K and reverse voltages, which are measured at -0.5 mA/mm of gate current is -6 mV/K. The temperature-dependence of pinch-off voltage is -1.01 mV/K and leakage current is 0.043 muA/K. Comparisons of noise performance including minimum noise figure and associated gain between In0.49Ga0.51P/In0.15Ga0.85As and Al0.25Ga0.75As/In0.15Ga0.85As low noise PHEMTs are also created. It is found that the high temperature performance of In0.49Ga0.51P/In0.15Ga0.85As PHEMT is much better than that of Al0.25Ga0.75As/In0.15Ga0.85As due to the less effects of deep level traps by absence of deep-complex (DX)-center and lower leakage current by higher Schottky barrier and valence band discontinuity. (C) 2003 Elsevier Ltd. All rights reserved.