In the manufacture of semiconductor products, overlay is one of the most critical design specifications. Overlay is the position of a pattern relative to underlying layers, and overlay control largely determines the minimum feature size that may be incorporated into semiconductor device designs. Overlay control must be performed on a run-to-run basis, i.e. at the end of run when product characteristics are available because they cannot be directly measured during a run. In this research a process model and a run-to-run control scheme was developed for overlay control, based on linear model predictive control (LMPC), and successfully implemented in a commercial facility. Performance monitoring of the closed-loop process was also carried out.