We have investigated the electrostatic and coherent couplings in 30 nm x 30 nm x 40 nm nanocrystalline silicon side gated point-contact transistors where the nanocrystalline silicon grains (10-35 nm in size) formed naturally coupled quantum dots through the thin grain boundary layers. Measurement at 4.2 K of the current as a function of the gate voltages in some thermally oxidised and high temperature annealed devices showed switching of the Coulomb oscillation peaks that was associated with electrostatic coupling between two major nanocrystals embedded in the point-contact channel. We also observed in similar measurements, using an oxidised-only device, an enhanced switching of the peaks with additional peak structures in the switching region where the grains coupled strongly. The characteristics in this region were well fitted to a sum of four Lorentzian peaks. These peaks were associated with coherent tunnelling of the electrons through the delocalised electron wavefunctions over the strongly coupled grains across the low and thin grain boundary tunnel barriers. (c) 2005 Elsevier B.V. All rights reserved.