The fabrication of a nanoscale gated quantum wire in a GaAs modulation doped field effect transistor substrate is described. Both the wire conduction channel, with a 110 nm physical width, and the gates were patterned into the two-dimensional electron gas of the substrate. This scheme produced in-plane gated devices with 110 nm gate lengths and 75 nm separations between the active areas. Electron-beam lithography was used to define masks for a subsequent flood exposure step with low energy argon ions (150 eV). This ion exposure technique produced very high gate-to-wire isolation, typically greater than 10(14) OMEGA at 4.2 K. The in-plane design employed here drastically reduces gate capacitance compared with metal top-gate designs, and promises ultrafast switching times. These devices showed no short channel punch-through effects, exhibited low gate leakage, and had sufficient gain to permit integration of several such devices into more complex circuits such as logic gates.