Low-frequency noise in GaAs-based nanowire field-effect transistors (FETs) controlled by a Schottky wrap gate (WPG) is investigated focusing on the size dependence of 1/f noise and the basic behavior of a gentle slope of the noise spectrum at a relatively high frequency. 1/f noise is found to systematically depend on the nanowire width W and gate length LG, which is explained by the conventional flicker noise model. The evaluated flicker noise coefficient KF is on the order of 10-23 V2 F, comparable to that of Si metal–oxide–semiconductor (MOS) FETs. The gentle slope close to 1/f0.5 frequently appears in the noise spectrum from the fabricated devices. Its intensity is found to be proportional to gate leakage current, suggesting that electrons flowing through the AlGaAs barrier layer induce generation-recombination (GR) noise in the gate region.