We report here the bulge testing results of both dense and porous poly-arylethers (PAE) polymeric low dielectric constant thin films. These films were prepared on a 4.7-μm-thick Si membrane window of 1600× 1600 μm2. The Si membrane was subsequently removed in a pulsed XeF2 etcher and the remaining thin film became the bulge test sample. The biaxial moduli of both the dense and 40% porosity low-k PAE thin films were measured to be 6.40±0.35 and 3.53±0.70GPa, respectively. These biaxial moduli, when combined with the thermal stress data of these films, enabled us to estimate the thermal expansion coefficients in the range of 26.8-32.6 and 56.1-72.5 ppm/°C for the dense and porous PAE films, respectively.