A multipeak negative-differential-resistance(NDR) device which comprises a singl e-electron transistor (SET) and a metal-oxide-semiconductor field-effect-transis tor (MOSFET) can achieve infinite number of peaks in principle. The MOS device e liminates the large SD voltage dependence of the peak and volley currents of the SET. The multipeak NDR device can be widely used in multiple-valued logics, and analog-to-digital converters (ADCs). We obtain a multiple-valued memory unit th rough the multipeak NDR device. And by using the folding I-V characteristic, a four-bit ADC is achieved. Compared with the traditional flash ADC, the SET-MO SFET ADC is very simple.