We present a new analytical charge conserving capacitance model for high electron mobility transistors (HEMTs) based on the quasi-static approximation and a proper partitioning of the channel charge between the source and the drain terminals. Simple analytical expressions for three terminal charges (Qg, Qd, and Qs) were derived by integrating the sheet charge density over the gate length. This leads to a total of nine so-called transcapacitances by taking derivatives of the terminal charges with respect to the voltages at three nodes. The nine transcapacitances can be organized into a 3×3 matrix obeying Kirchhoff's current law and independence of reference. The transcapacitances are non-reciprocal in nature, i.e. Cij≠Cji when i≠j. The model is valid both above and below threshold and shows good agreement with experimental data.