This paper presents a qualitative explanation of the dependencies of the AlGaN/GaN HEMT’s intrinsic capacitances on the terminal voltages. For that, a simplified 1-dimensional model of the HEMT’s channel was derived, which reduces the device physics to a minimum that is easily understandable but that still retains the HEMT’s basic operation. The proposed model demonstrates how the lumped intrinsic capacitances of the conventional equivalent circuit model, Cgs, Cgd, and Cds are completely defined by the free electron concentration variation within the channel. Then, it is shown that the emergence of apparent non-physical capacitances, such as a negative Cds in the equivalent circuit the Y-matrix, is simply a consequence of the abstraction of the charge spatial distribution into some lumped terminal capacitances.