A method and apparatus for using photoemission to determine the endpoint of a dry etch process. In one embodiment, the endpoint of a dry etch process is determined when the dry etch process is acting on a substrate comprising a layer of a first material overlying a second material. The substrate is illuminated with a beam of monochromatic light. The photon energy of the monochromatic light is greater than the work function of one of the two materials, and less than the work function of the other material. Thus the beam of light is capable of inducing photoemission of electrons in only one of the two materials: the material with a work function less than the photon energy of the beam of light. The electrons emitted by the photoemitting material are collected. The current generated by the collected stream of electrons, the photocurrent, is amplified. A time-series of amplified photocurrent measurements is monitored for changes that correspond to the endpoint of the dry etch process.