Chemically assisted ion beam etching (CAIBE) is widely practiced in the semiconductor industry. In the electron microscopy field, the CAIBE technique offers a new method for preparing specimens that are difficult to make by conventional inert gas milling techniques, e.g. indium containing type III-V compound semiconductors. CAIBE employs a collimated, molecular beam of a reactive species, e.g. iodine in combination with a conventional inert gas fast atom beam for thinning TEM specimens. CAIBE should not be confused with reactive ion beam etching (RIBE) which takes a chemically active species (e.g. iodine) and converts it into a beam of fast ions directed at the sample. CAIBE has three major advantages over (RIBE): i) corrosion of the ion gun components does not occur, ii) much smaller quantities of reactive gas are required and hence pump maintenance and pollution problems are minimized, iii) a wider range of chemicals may be used. Superior results are obtained if CAIBE is done on only one side of the specimen at a time. This is achieved using a new type of specimen holder post which enables very low angle milling and minimizes specimen contamination by sputtering from the holder. This new technique is described and results from iodine CAIBE milling, iodine RIBE milling and argon ion milling are compared for InP, InSb and GaAs as well as metals like tungsten. Also, the beneficial effects of very low angle (∼1°) argon ion milling in preparing specimens of silicide containing Si based IC wafers is reported.