Bismuth sulfide quantum dots (phi similar to 12 nm) with two-dimensional platelet morphology synthesized using a simple aqueous colloidal method exhibit directional growth along (2 1 1) direction. Impedance characteristics of this two-dimensional quantum structure yields a characteristic semi-circular profile due to a classical Voigt element in addition to a semi-circle like loop in the negative imaginary part of the impedance Nyquist plot. The apparent inductive reverse-loop impedance profile observed, a distinguishing feature of this study can be explained on the basis of an unusual negative resistor-capacitor combination, realized due to relaxation of surface states in this technologically important semiconductor-quantum structure. (C) 2010 Elsevier B.V. All rights reserved.