We focus on slow de-trapping phenomena in AlGaN/GaN MIS-HEMTs with a bilayer dielectric (in-situ Si3N4/Al2O3) with two different thicknesses of in-situ Si3N4 (10 nm and 5 nm). By using a "filling pulse" at a positive gate voltage, a trap with activation energy of 0.69-0.7 eV was identified to be responsible for the V-TH shift. Based on literature, filling conditions, and the simulated band diagrams, this trap is most probably located at the interface between the dielectrics and AlGaN barrier. A physical model is proposed to explain the V-TH shift due to the trapping/de-trapping phenomena based on the occupation dynamics of donor traps at the interface between the in-situ Si3N4/Al2O3 and the AlGaN barrier. (C) 2014 Elsevier Ltd. All rights reserved.