Large polycrystalline silicon membranes in the form of bridges suspended over deep monocrystalline silicon cavities have been fabricated by using porous silicon as a sacrificial layer. Stresses within the free-standing membranes as well as within supported polycrystalline membranes (pads) are measured through micro-Raman spectroscopy and a different model is used in each case in order to calculate the stresses from the observed Raman shifts. A detailed study of stress distribution along the membranes and pads has been performed, as a function of thickness and annealing treatment. The stress profiles reveal variations in stress along the membranes and pads.