Abstract  The mechanical deflection of circular membranes of SiN _x is presented as a technique for measuring the stiffness and residual stress of very thin, single-layer films. The dimensions of the membranes are controlled precisely using standard photolithography, dry etching and wet etching techniques. Thicknesses vary between 0.09 μm and 0.27 μm and average diameters range between 1100 μm and 4100 μm. A Nanoindenter is used to deflect the membranes with a point force at their centers, and to continuously record the applied forces and the resulting deflections. The analysis of the force-deflection data yields the values of Young’s moduli and residual stresses for the films.