In this paper, the trap signatures located at the GaN cap/SiN interface and in the GaN buffer are clearly identified in the Fe-doped AlGaN/GaN HEMT device by means of low frequency (LF) S-parameter characteristics. For that, LF Sparameter TCAD Sentaurus physics-based 2D simulations are performed for different temperatures ranging from 25°C to 75°C. In fact, the imaginary part of Y22 allows to extract the buffer trap parameters, while the imaginary part of Y21 provides a quantitative information of the traps located at both surface and buffer regions. An excellent agreement between measurement and simulation of Y21 parameter is obtained in this work. An activation energy of Ea= 0.45 eV and a cross section around σn=3×10-16 cm 2 are identified for buffer traps. The computed parameters for the surface traps are ED = ~0.3 eV and σD = ~5×10-18 cm 2 .