This study presents a qualitative analysis on gain compression phenomenon of integrated power MOS transistor. In the large-signal operation of power device, the gain compression plays an essential role for characterizing non-linear behavior. The proposed approach combines both the RF waveform and load line characteristics in different quiescent points. Experimental results demonstrate the approach is feasible. The analysis of gain compression corresponds to different quiescent biases is useful during the implementation of power device for RFIC application.