The quantum tunneling effect is a direct consequence of the Heisenberg uncertainty principle and is most pronounced for light particles, such as electrons, whose de Broglie wavelength is comparable to the tunneling distance. Initially discovered for trapped electrons, long-range electron tunneling gradually defined many diverse research fields including scanning tunneling microscopy, molecular electronics, and DNA sequencing. A significant body of the electrochemical tunneling studies have involved the following two approaches of modifying conducting electrodes: self-assembled monolayers of redox species tethered to an insulating alkyl chain, or insulating polymer films with a redox mediator in solution. hBN provides an inorganic alternative with a precise control of the tunneling distance, especially within the subnanometer regime, unattainable even for the state-of-the-art tunneling layers of Al 2 O 3 grown by atomic layer deposition at thicknesses of ~1 nm. Additionally, the high crystallinity of hBN and short barrier length ensure scattering-free ballistic electron tunneling and therefore no ohmic heating within the dielectric. It is therefore not surprising that hBN has been utilized as a tunneling barrier in solid state devices. This has included hBN being sandwiched between two metals, two graphene/graphite layers, and a metal and graphene. Most of these studies found that the tunneling current increases exponentially with the applied voltage and decays exponentially with the hBN thickness to negligible levels for ~6-layer hBN. Both experiments and theory suggest that hBN is not simply a passive insulating barrier but rather that it affects the tunneling through carrier interactions with phonons, defects, and dopants. Herein, we employ atomically-flat hBN as a tunneling barrier to an electrochemical reaction between a redox mediator in a liquid solution and a graphite electrode (Figure ). We make use of electron-beam (e-beam) lithography to fabricate inlaid disk ultramicroelectrodes and employ a modified microdroplet electrochemical cell technique, described elsewhere. The use of a high-quality, crystalline 2D insulator has some advantages over the two traditional tunneling approaches described above, owing to the chemically inertness of hBN, the lack of dangling bonds on its basal plane surface, and a microscopic size of the tunneling area. These characteristics lead to an atomically-flat electrode surface, well-defined control of the tunneling distance via the number of hBN layers (N), significant reduction in the occurrence of pinholes and defects, and 'simplicity' of an inorganic tunneling barrier, contrasting with the complexity of organic barriers, which possess discrete molecular energy levels and specific chemical interactions. The steadystate voltammograms of [IrCl 6 ] 3-oxidation and [Ru(NH 3 ) 6 ] 3+ reduction in this system exhibit the expected exponential dependence of the electron transfer rate on the tunneling distance for monolayer (1L) and bilayer (2L) hBN. However, significant deviations in the measured electrochemical parameters are observed for thicker hBN due to the manifestation of the Marcus-Hush theory. We further rationalize the results based on the density functional theory (DFT) calculations of the energy levels in the graphite/hBN/liquid heterostructure.