Field desorption has been used successfully to produce clean germanium patterns in the electron field emission microscope. The field-cleaned pattern transforms upon annealing to one very similar to that obtained from silicon cleaned by heating in vacuum. Changes in impurity concentration at the surface during cleaning, heretofore a problem, are avoided by the desorption technique. Surface atom mobility becomes appreciable at ~250°C on clean germanium and at ~ 800°C on clean silicon. Field emission current-voltage characteristics for both clean Ge and Si are presented. The results are discussed in the light of existing theory, and the need for a theory including emission from surface states and the valence band is pointed out.