The dependence of PHEMT's drain current and gain on temperature were analyzed.It was found that the current and gain decreased with temperature increase.Two methods were presented for automatically compensating the temperature dependence and their principals were analyzed.A series source resistor could keep the PHEMT's drain nearly unchangeable and decrease the temperature effect on the amplifier gain to some content.However

the automatic gate voltage temperature compensation was a strong compensation.It increased the gate voltages and PHEMT's transconductance with the temperature increase

thus greatly decreased the temperature effect on the gain.The two methods were then combined and applied to a broadband low noise amplifier.Good experimental results were obtained.When the temperature increased from -55℃ to +85℃ and from -55℃ to +125℃

the amplifier gain drop decreased by 60% and 51% at 6 GHz

respectively

which greatly improved the gain-temperature feature of the amplifier.