DC and pulsed transfer characteristics of AlGaN/GaN high electron mobility transistors (HEMTs) have been systematically investigated. A significant difference of transconductance linearity between DC and gate-pulsed measurements is clearly observed. The acceptor-like traps in the barrier layer under the gate is the main cause of non-linear behavior of AlGaN/GaN HEMTs transconductance. A physical model has been constructed to explain the phenomenon. In the modeling, an acceptor-like trap concentration of 1.2 x 10(19) cm(-3) with an energy level of 0.5 eV below the conduction band minimum shows the best fit to measurement results. (C) 2015 Elsevier Ltd. All rights reserved.