A semimetal to semiconductor transition in low-dimensional Bi nanowires is theoretically predicted based on the quantum confinement effect, which results in the enhancement of the thermoelectric performance. However, this transition has rarely been observed in the transport properties of gate modulation because of there being too few charge carriers induced by a typical electric field effect. In this paper, we report on our observations of the on-off state in a Bi nanowire using a polyethylene oxide/LiClO4 electrolyte gate, which produces a much larger effect than a back-gate. The carrier density of the surface state was found to be consistent with previously reported results. The intrinsic properties of the Bi nanowires, as obtained by temperature- and diameter-dependent gate modulations, are also discussed.