In this paper, the micro-Raman technique was used to measure the residual stress and its variation in Si MEMS devices and carried out on two platforms. Firstly, it was observed that there is a good correlation between the wafer's centre deflection and Raman shift. Secondly, using diaphragms fabricated from a 501 wafer, it was observed that a thinner diaphragm results in more Raman shift and vice versa. After a thin metal film layer (Cr/Au) is sputtered onto the diaphragm, it was observed that the Raman shift is more significant as the metal layer represents an amplification effect. These results show that the micro-Raman technique is a powerful method to investigate the residual stress of Si MEMS devices, especially how the stress changes during the fabrication process. All these could help select and optimize the fabrication parameters during the device manufacturing process. (C) 2009 Elsevier B.V. All rights reserved.