GaN material holds an advantageous position in the fabrication of power devices. This advantage is manifested by the possibility to perform GaN based devices working in high voltage, high current, high frequency and high temperature conditions. However, despite these theoretical forecasts, trapping mechanisms limit the performances of the GaN based devices revealed by the so-called “drain current collapse”. Our study is based on a methodology to understand trapping mechanisms in GaN metal-insulator-semiconductor high-electron mobility transistors. This work was achieved by means of electrical and optical characterization techniques such as Fourier transform deep level transient spectroscopy and photoluminescence. The activation energy and the apparent capture cross section of eight traps were extracted in normally-off (Ids=0A when Vgs=0V) AlGaN/GaN heterostructure technology used for power conversion. Six of these traps, E1=0.16eV, E2=0.31eV, E3=0.46eV, E4=0.5eV, E5=0.64eV and E6=0.79eV are electron traps located in the channel. An identification has been proposed for each trap. Two hole-like traps, H1=0.17eV and H2=0.74eV were assigned to the Mg and C doping of the GaN buffer layers, respectively. These traps might play a role in the current collapse which appears after the application of a large reverse voltage on the gate of the device. Furthermore, the results obtained using electrical and optical techniques allowed concluding that oxygen atoms and dislocations are incorporated in GaN layers during the growth.