We report on the development of a test bench to extract pulse-to-pulse (P2P) stability On-Wafer in Ku-band. The P2P stability is crucial for RADAR performances. GaN HEMT transistors are a promising candidate for RADAR application. However, they typically generate trapping effects, which can strongly affect the P2P stability. Two methods RMS and Standard Deviation based on temporal analysis are employed to extract the stability indicators. The main idea of the P2P test bench is the use of a homodyne demodulation to recover the envelop of the RF. This setup is also combined to an active load pull towards P2P stability test bench dedicated to the new generation of GaN HEMT transistors in large signal condition close to their operational mode.