This paper addresses the simultaneous determination of the Young’s modulus and the residual stress of thin silicon nitride films deposited by dual frequency plasma enhanced chemical vapour deposition, to be used in the fabrication of free-standing MEMS membranes. Load–deflection tests of circular membranes and measurements of the deformation of free-standing microbeams due to the internal-stress release were performed; parallely the microstructures were modelled by finite element analysis as a function of the Young’s modulus and the internal stress. For each test structure a set of values of the Young’s modulus and the internal stress was found and from their comparison the values for the deposited film can be determined.