A method of producing lateral confinement of an electron gas has been realized by using molecular beam epitaxy to grow a high mobility heterostructure on a (100) n+-GaAs layer selectively etched to create a two-dimensional array of cavities through the n+-GaAs, which are bound by higher index facets. Far-infrared cyclotron resonance (CR) spectra unambiguously demonstrate that the electron gas formed inside the cavities is confined in both lateral directions. Typical confinement energies of 30 cm-1 and widths of 2000 nm are derived from the spectra and magnetoresistance measurements. The effect of different n+-GaAs backgate biases is also investigated. Combining information from CR spectra with atomic force microscopy images provides a picture of the nature of the lateral confinement in this structure. © 1997 American Institute of Physics.