Thermal desorption spectra from single crystal planes of a field emitter are obtained with the technique described. The specimen temperature is varied linearly and the field emission current from the face of interest is recorded vs temperature. Heating current and temperature measurements are transmitted to and from the tip using digital techniques via fiberoptic links to assure the high isolation necessary. A microcomputer is used to control the entire system, produce the linear temperature sweep, and acquire and treat the data. The desorption of hydrogen from the (111) plane of field-evaporated tungsten is presented as a test of the technique; a comparison between our spectra and the data reported in the literature shows a good correlation between the field emission and the classical thermal desorption spectroscopy. A good facet selectivity is obtained as proved by a result concerning H2 on W (210).