Abstract. Development of new genetic approaches to either interfere with the ability of mosquitoes to transmit dengue virus or to reduce vector population density requires progressive evaluation from the laboratory to contained field trials, before open field release. Trials in contained outdoor facilities are an important part of this process because they can be used to evaluate the effectiveness and reliability of modified strains in settings that include natural environmental variations without releasing mosquitoes into the open field. We describe a simple and cost-effective semi-field system designed to study Aedes aegypti carrying a dominant lethal gene (fsRIDL) in semi-field conditions. We provide a protocol for establishing, maintaining, and monitoring stable Ae. aegypti population densities inside field cages.