Abstract: Method and system for estimating a concentration of free electrons with a selected spin polarization in a semiconductor material. A static magnetic field and an electromagnetic field are impressed on the semiconductor, and free electrons are injected (through diffusion or tunneling) into the semiconductor material from a ferromagnetic material. Motion of the injected, spin-polarized electrons, within the semiconductor gives rise to a Hall voltage across the semiconductor. This voltage is measured at one or more spaced apart locations and analyzed to detect presence of, and estimate a concentration of, free electrons with a selected spin at at least one location within the semiconductor. Effects of an imposed stress, temperature, illumination or electromagnetic field on the semiconductor can be determined.