This paper demonstrates normally-off dual gate AlGaN/GaN MISFETs with a selective area-recessed floating gate fabricated on the AlGaN/GaN-based heterostructure with an AIN insertion layer. For the fabrication of the dual gate structure, the AlGaN layer in the control gate region was fully recessed and then an Al2O3 layer as a gate dielectric was deposited by the atomic layer deposition method, which ensures the normally-off operation and greatly decreases the leakage current. An additional floating gate with selective area-recessed patterns, which is located between the control gate and the drain electrode, was employed to enhance the breakdown voltage. The fabricated normally-off dual gate AlGaN/GaN MISFET exhibited a threshold voltage of 2 V, a high I-ON/I-OFF ratio of 3 x 108 at a drain voltage of 10 V, a maximum transconductance of 88 mS/mm at a gate voltage of 5.8 V, a drain current density of 364 mA/mm at a gate voltage of 8 V, and a breakdown voltage of 880 V. (C) 2014 Elsevier Ltd. All rights reserved.