An improved hybrid parameter‐extraction technique is proposed for the small‐signal modeling application in AlGaN/GaN high electron mobility transistors (HEMTs). The capacitance partitioning characteristics of cold pinch‐off GaN device with non‐field‐plate and field‐plate structures are reinvestigated and the scanning range of parasitic capacitances Cpg and Cpd is determined. A systematic optimization approach is proposed to obtain the initial values of Cpg and Cpd. By using the global optimization algorithm, particle swarm optimization, the reliable parasitic parameters can be acquired based on the proposed error function. The validity of the developed hybrid parameter‐extraction method is verified by 2 × 100 μm AlGaN/GaN HEMT with source‐connected FP structure from 0.1 to 40 GHz among the 442 biasing points.