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This paper presents junction temperature estimation method of direct-drive Gallium Nitride (GaN) high electron mobility transistors (HEMTs) in two-

level inverters for driving a permanent magnet synchronous motor (PMSM). GaN HEMTs exhibit high electron mobility due to the formation of two-

dimensional electron gas (2DEG) between the GaN layer and the AlGaN layer. GaN HEMT is a positive polarity device that has a normally-on 

characteristic by which the switch remains in on-state even when no gate voltage is applied. It is necessary to implement a normally-off 

characteristic for GaN HEMTs to be applied in a power conversion system (PCS). The operation of a PCS generates power losses in GaN HEMTs, 

which are transformed into thermal energy. The junction temperature of GaN HEMTs affects various electrical properties, including on-resistance, 

switching energy, and V-I characteristic. Therefore, the power loss profile should account for variations in the electrical properties. An RC Cauer 

network is used to model the thermal behavior. The power losses are converted into junction temperature based on the characteristics of the 

materials that are both internal and external to the GaN HEMTs. The validity of this junction temperature estimation method is verified through 

simulation and experimental results.