To produce well-defined device structures having ultrasmall areas in compound semiconductors, it is necessary that lateral variations in doping and composition be realizable having interfacial quality comparable to that presently achieved vertically with techniques such as molecular beam epitaxy (MBE). This letter describes a novel scheme involving the controlled, patterned sublimation of GaAs, termed submicron lithography by molecular evaporation (SUBLIME), which is performed in situ within a MBE growth chamber. The strong orientation dependence of the removal rate from (100) substrates is discussed and final morphology is shown to be critically dependent on both substrate temperature and incident As flux. Several materials have been used successfully as patterned masks, and Al0.3Ga0.7As has been demonstrated to be a versatile SUBLIME]] etch stop." High-resolution micrographs of the resulting submicron structures are shown and initial results from studies of dopant redistribution and in situ regrowth after patterning are presented. Finally, some implications for future device fabrication are discussed.