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 S-parameter TCAD Sentaurus physics-based 2D simulations are performed for different temperatures ranging from 25\mathrmC to 75\mathrmC. In fact, the imaginary part of Y_22 allows to extract the buffer trap parameters, while the imaginary part ofY_21 provides a quantitative information of the traps located at both surface and buffer regions. An excellent agreement between measurement and simulation ofY_21 parameter is obtained in this work. An activation energy ofEmathrma=0.45 eV and a cross section around σn=3× 10-16cm2 are identified for buffer traps. The computed parameters for the surface traps are ED =∼ 0.3 eV and σ 0=∼ 5× 10-18cm2.