Based on I - V characteristics of single-electron transistor and the idea of MOS digital circuit design, an inverter using the single-electron and MOS transistors is proposed and some other logic gate circuits are educed. Finally a novel half adder circuit is realized using these logic circuits. The half adder circuit, in comparison with the pure CMOS circuit, has the advantages that the number of transistor is decreased, the structure of the circuit is predigested, and the total static power consumption is reduced. The accuracy of the circuit is validated by SPICE.