A simple method, based on overlapping the dosage distribution of the discretely electron beam written nano-dots, was employed to fabricate nano-structure containing narrow constrictions. From the appropriately designed electron beam process, the electron dosage in the overlapping region is just above the threshold exposure dosage of the negative electronbeam resist. A Si-based nano-dot with two narrow tunnel junctions called single electron transistor was formed after dry etching and thermal oxidation process since the overlapping region is much narrower than the diameter of the nano-dot. The electric characteristic of the SET was found to be consistent with the expected behavior of electron transport through a gated quantum dot. Also, The characteristic phase diagrams of double dot structure were obtained by independently sweeping two gates. The honeycomb lattice of the conductance resonances in the phase diagram was modeled using a capacitance equivalent circuit and the electronic behavior of the double dot device was discussed from measured charging diagram comparing with the model.