In situ non-invasive process monitoring and control during semiconductor epitaxy is a potential enabling technology that can transform the existing approach to epi-wafer manufacturing. In this paper, we describe the implementation of a multi-sensor system consisting of both process- and wafer-stage sensors on a multi-wafer production molecular beam epitaxy (MBE) tool. We also illustrate through a few examples how these sensors are used for device and calibration growth. Finally, we will discuss some challenges facing 3 sensor-based MBE system under a. production environment.