The magnitude and origin of residual stresses in thin polysilicon MEMS structures are discussed in this article. The curvature of polysilicon beams were determined at different temperatures. An accurate method of analysis that avoids the thick substrate approximation is described. The polysilicon beams without an Au layer exhibited temperature-independent curvatures, indicating that their residual stresses were largely process related. Beams with an Au top-coat exhibited a strong temperaturedependent effect, and allowed derivation of a stress-free temperature of 143°C. The technique allowed an independent estimate of the thermal expansion coefficient of polysilicon, namely 2.5×10−6 to 3.1×10−6/°C.