Factors affecting the fracture strength of single-crystal silicon membranes are assessed. These factors include: membrane shape at the membrane's intersection with structural frames or sidewalls, membrane thickness, membrane surface roughness, membrane mis-orientation to the principal crystallographic axes, wafer starting material quality, membrane stress (or pre-tension), and microstructure and shape at bond interfaces, such as the anodic bond interface between membrane and Pyrex wafers. Measurements of fracture strength versus these factors are made. Direct measurements of stress are also made using micro-Raman techniques. Simulations of membrane structures are studied, in order to evaluate the measurements. The results indicate that the predominant factor affecting fracture strength is surface roughness.