This paper proposes a SPICE model development methodology for quantum-dot cellular automata (QCA) cells and presents a SPICE model for QCA cells. The model is validated by simulating the basic logic gates such as inverter and majority voter. The proposed model makes it possible to design and simulate QCA combinational circuits and hybrid circuits of QCA and other NANO devices using SPICE. In the second half part of the paper, SET and QCA co-design methodology is proposed and SET is used as a readout interface of the QCA cell array. The SET and QCA hybrid circuit is a promising nano-scale solution. q 2006 Elsevier Ltd. All rights reserved.