The nanofabrication of two-dimensional photonic lattice structures in GaAs/AlGaAs is reported. The nanofabrication procedure combines direct-write electron-beam lithography and reactive-ion-beam etching to achieve etched features as small as 50 nm. The lattice comprises a hexagonal array of air cylinders etched into a semiconductor surface with a refractive index contrast of 3.54. A range of air volume fractions from 14% to 84% was investigated. The lithographic, masking, and etching processes necessary to fabricate the lattice are described along with practical limitations to achieving a lattice of arbitrary air volume fraction. Initial results from optical characterization of the lattice are also presented.