Abstract: The present invention relates to a system for the manufacture of semiconductor devices by lithography, and in particular to an assembly of mask containers for use in such a system. The system comprises: a plurality of mask containers adapted to engage with one another such that two or more containers can be carried together as a stack; a plurality of lithography bays; a transport rail system for carrying the containers between different lithography bays. Each lithography bay has a transmitter/receiver unit for communicating lithography data with a tracking device located in each container, allowing for more efficient mask management. The transportation of the containers in stacks results in an improvement in efficiency.