The mechanical properties of organosilicate glass (OSG) thin films were measured for the first time using bulge testing of OSG / silicon nitride (SiNx) freestanding membranes. Evaluation of two different OSG films revealed significant differences in Young's modulus and residual stress between the two dielectric films. Young's modulus of both types of OSGs was independently measured using nanoindentation and found to be at least 8.5-17% greater than that measured using the bulge test. It is well known, and demonstrated herein, that modulus data obtained from nanoindentation is influenced by mechanical properties of the substrate. Operating without this constraint, it is believed that data obtained using the bulge test more accurately represents the intrinsic mechanical properties of OSG thin films.