Transmission line pulses (TLP) with 0-60V amplitude and 100ns pulse width have been applied for accelerated lifetime tests of GaAs devices. 1/f noise, RF noise and I/V measurements are applicable for the characterisation of the reliability of these devices. Different failure mechanisms can be identified by applying square pulses of varying amplitude and different polarity on a variety of samples. Correlation between anomalies in 1/f noise, RF noise and I/V characteristics has been determined. Using this novel method, the determination of failure threshold levels for current density, electric field and charge carrier temperature is possible and critical spots in device design can be ascertained.