In this work, the gate-to-channel leakage current in FinFET structures is experimentally studied in comparison with quasi-planar very wide-fin structures, and as a function of the fin width. Devices with both doped and undoped channels and different gate stacks are studied. Experimental evidence for the reduction of gate tunneling current density in narrow FinFET structures compared to their counterpart quasi-planar structures is reported for the first time. This gate current reduction is observed for both n-channel and p-channel devices and is found to be stronger for HfO2 than for SiON. For a given gate dielectric, the above gate current improvement in FinFETs enhances with decreasing the fin width. For SiON with an equivalent oxide thickness of 1.6 nm in undoped n-channel devices, it varies from factor of 2.3-4.3, when the fin width decreases from 75 to 25 nm. The possible reasons for the observed effect are discussed. (C) 2007 Elsevier Ltd. All rights reserved.