High-electron-mobility transistor (HEMT) is a promising device for power applications because of their high breakdown voltage, high electron mobility in two-dimensional electron gas (2DEG) area, fast switching capability, high-temperature operating capabilities, compatibility with standard electronic circuits, and low production cost. In contrast to the gate in metal–oxide–semiconductor field-effect transistor (MOSFET), which extends from source to drain, the gate in HEMT splits the device into two main sections: field-effect (section under the gate) and resistive (section outside the gate). Resistances of the 2DEG outside the gate sections are constant and modelled by fixed resistors. However, the 2DEG resistance under the gate section is dependent to the gate voltage, which can be modelled by channel resistance of a field-effect transistor (FET). Since these resistances depend on the mobility of electrons in the 2DEG, it is important to separate the electron mobility in the resistive and field-effect sections. Therefore, existence of the resistive section in the HEMT structure leads to requiring new methods for the HEMT mobility measurement. Also, since there is no model for the HEMT in SPICE, novel models are required for the SPICE simulation of the HEMT. In order to solve these issues: