A new 22-element small signal equivalent circuit model for the AlGaN/G N high electron mobility transistor(HEMT) is presented. Compared with the traditional equivalent circuit model, the gate forward and breakdown conductions(G_(gsf) and G_(gdf)) are introduced into the new model to characterize the gate leakage current. Additionally, for the new gate-connected field plate and the source-connected field plate of the device, an improved method for extracting the parasitic capacitances is proposed, which can be applied to the small-signal extraction for an asymmetric device. To verify the model, S-parameters are obtained from the modeling and measurements. The good agreement between the measured and the simulated results indicate that this model is accurate,stable and comparatively clear in physical significance. A new 22-element small signal equivalent circuit model for the AlGaN / GN high electron mobility transistor (HEMT) is presented. Compared with the traditional equivalent circuit model, the gate forward and breakdown conductions (G_ (gsf) and G_ (gdf)) are introduced into the new model to characterize the gate leakage current., for the new gate-connected field plate and the source-connected field plate of the device, an improved method for extracting the parasitic capacitances is proposed, which can be applied to The good agreement between the measured and the simulated results indicate that that model is accurate, stable and comparatively clear in physical significance .