Random arrays of CsCl hemispherically shaped islands with average diameters as small as 500 Å have been made on n+GaAs substrates. The CsCl behaves as a resist of high selectivity when the GaAs is reactively ion etched in a BCl3 plasma. The resulting structure is a set of pillars all the same height, but with varying diameters, typically ±15% of the average value, 〈D〉. Typical pillar packing density, S, is 20%. Photoluminescence (PL) studies were made at 10 K on n+ and semi‐insulating GaAs using 514.5 nm exciting radiation. PL spectra from n+GaAs structures of 〈D〉=520±78 Å, h=800 Å, S=20%; 〈D〉=610±97 Å, h=450 Å, S=12%; 〈D〉=1215±210 Å, h=600 Å, S=20%, as well as a plane surface, are reported. There is a shift in the peak value of the PL curves with respect to the planar structure of 26, 13, and 2.5 meV, respectively. It may be possible to understand these shifts in terms of quantum confinement effects if the effective pillar size is reduced by surface space charge effects.