Facet formation during the growth by molecular beam epitaxy of GaAs microstructures on pre-patterned GaAs(0 0 1) substrates has been investigated by secondary electron microscopy and atomic force microscopy. The effects of the growth conditions have been studied for structures formed on both stripe and square based mesas. In all cases {1 1 0} facets are formed suggesting that kinetics plays a key role in determining the shape of the resulting microstructure. We show that by optimising the growth conditions it is possible to produce high quality pyramidal microstructures that appear to have the appropriate characteristics for application as a corner cube mirror in optoelectronic device applications.