A novel electroabsorption modulator based on tuning the Fermi level relative to mid-gap states in a semiconductor. The modulator includes a semiconductor waveguide that has an input port and an output port. Between the input port and the output port is a section of the waveguide that functions as an electroabsorptive region. Adjacent to the electroabsorptive region are electrical contacts. In operation by adjusting voltages on the electrical contacts, the quasi-Fermi level in the electroabsorptive region of the semiconductor waveguide is brought above or below mid band-gap electronic states. As these states transition between occupancy and vacancy, the absorption coefficient for optical radiation in the electroabsorptive region of the semiconductor changes. As this change in absorption coefficient modulates the intensity of transmitted radiation in response to an input data stream driving the voltages, the device functions as a semiconductor optical modulator in accordance with the principles of the invention.