We report on the fabrication of n-AlGaAs/GaAs constricted-channel field-effect transistor (FET) structures by focused ion beam (FIB) implantation, and study transport properties of low-dimensional electrons via FIB induced localized states. In this work, quantum wire FET samples with in-plane gates and top gate were formed by using a focused Ga ion beam by which Ga ions of a high dose density (>10(15) cm(-2)) are introduced in the vicinity of a conductive channel at room temperature. The drain conductance G(d) was studied in constricted channels with various nominal widths, W. It is found that G(d) Of a narrow channel (W-l mu m) becomes quite small and nonlinear at low temperatures. When G(d) is measured as a function of gate voltage, V-g, periodic oscillations are clearly observed at 15 K with a typical spacing of V-g similar to 60 mV, whereas the oscillation weakens and transforms to steplike structures at higher temperature (250 K). This oscillatory characteristic may possibly result from single electron transport through quantum dots associated with FIB-induced random potentials in the channel.