A high performance gate-all-around (GAA) junctionless (JL) polycrystalline silicon nanowire (poly-Si NW) transistor with channel width of 12 nm, channel thickness of 45 nm, and gate length of 20 nm has been successfully demonstrated, based on a simplified double sidewall spacer process. Without suffering serious short-channel effects, the GAA JL poly-Si NW device exhibits excellent electrical characteristics, including a subthreshold swing of 105 mV/dec, a drain-induced barrier lowering of 83 mV/V, and a high I on /I off current ratio of 7 × 10 8 (V G = 4 V and V D = 1 V). Such GAA JL poly-Si NW devices exhibit potential for low-power electronics and future 3-D IC applications.INDEX TERMS Gate-all-around (GAA), poly-Si, junctionless (JL), nanowire (NW), sidewall spacer, transistor.