This paper investigates the electrothermal stress- induced performance degradation of a cascode low-noise amplifier (LNA) built using InGaP/GaAs heterojunction bipolar transistors (HBTs). Changes in device characteristics due to the electrothermal stress were examined experimentally. At the moderate base-emitter voltage, the base current increases and current gain decreases after stress. The SPICE Gummel-Poon (SGP) model parameters were extracted before and after stress and measured device data were used in the Cadence SpectreRF simulation to study the impact of electrothermal stress on the low-noise amplifier performance.