AlGaN/GaN FinFETs, with high quality atomic layer deposited (ALD) Al2O3 gate dielectric, have been fabricated. The devices have a two-dimensional electron gas (2DEG) channel formed at AlGaN/GaN heterointerface and two sidewall GaN MOS channels. Two distinct transconductance peaks can be observed, one for the 2DEG channel and the other for the sidewall GaN MOS channels. On the other hand, we present heterojunction-free GaN FinFETs with junctionless configuration. The current flows through the volume of the heavily doped GaN fin rather than at the surface channel, which leads to superior off-state performance and less drain-induced virtual substrate biasing (DIVSB) effect. (C) 2014 Elsevier Ltd. All rights reserved.