We analyze the channel and surface charge dynamics of a high voltage AlGaN/GaN Heterostructure Field Effect Transistor (HFET) operating as a power switch. We demonstrate that operation in the voltage range exceeding 100 V without field plates involves alternating of the surface compensating charge in the gate-drain spacing. Developed model predicts the switching speed limitation of power HFET determined by the surface recharge rate and provides new, voltage-scalable design approach of AlGaN/GaN power devices. (C) 2010 Elsevier Ltd. All rights reserved.