A sensor for measuring mechanical stress in a layered metallization structure such as the back end of line portion of an integrated circuit die is provided. The sensor operates as a field effect transistor comprising a gate electrode, gate dielectric, channel and source and drain electrodes, wherein the gate electrode is a conductor of a first metallization level and the source and drain electrodes are two interconnect vias, connecting the channel to respective conductors in an adjacent level. At least one of the interconnect vias is formed of a material whereof the electrical resistance is sensitive to mechanical stress in the direction of the via. The sensitivity of the electrical resistance to the mechanical stress is sufficient to facilitate measurement of the stress by reading out the drain current of the transistor. The sensor thereby allows monitoring of stress in the BEOL prior to cracking.