We investigated the effects of post-growth annealing on structural and optical properties of self-assembled ring-shaped GaAs quantum dots (QDs) by photoluminescence (PL) measurements and cross-sectional high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM). Marginal structural changes of the QDs were observed after the annealing process up to 800 degrees C while the intensity of PL emission increased drastically. The annealed laser structure with three layers of the ring-shaped QDs showed photo-pumped laser action with clear threshold at 77 K. (c) 2007 Elsevier B.V. All rights reserved.