InGaP/GaAs based Heterojunction Bipolar Transistors are becoming the leading device for a wide variety of applications including power amplifiers, high speed A/D converters, low noise receivers, and low phase noise oscillators. This device can be designed to operate from L-band to millimeter waves. The excellent reliability of InGaP HBTs at high current densities and high device junction temperatures offers increased performance margins for high frequency and high power applications. At J(c) = 25 kA/cm(2) and T-j = 264 C, no device failures were reported out to 10,000 hours. Reliability data extracted at a higher junction temperature of up to 360 C and at a current density of 60 kA/cm(2) showed an extrapolated MTTF of 5 x 10(5) hours at T-j = 150 C.