Laser-induced selected area epitaxy of CdTe thin films on GaAs substrates has been investigated and the role of vapour phase and surface reactions considered. Photo-enhanced growth rates of CdTe have been measured as a function of UV laser intensity and as a function of Cd to Te alkyl ratios. The growth rates are not simply determined by vapour phase photo-dissociation but also by a photolytic reaction on the surface. The latter enables good pattern definition where the growth rate is enhanced by the incident uv -radiation. The factors that determine the photo-enhancement are considered in the light of the Langmuir-Hinsheltwod model.