The frequent use of well known critical data handbooks like Beilstein, Gmelin and Landolt­ Bornstein is impeded by the fact that merely larger libraries - often far away from the scientist's working place - can afford such precious collections. To satisfy an urgent need of many scientists for having at their working place a comprehensive, high quality, but cheap collection of at least the basic data oftheirfield of interest the series "Data in Science and Technology"is started now. This first volume presents the most important data on two groups of semiconductors, the elements of the IVth group of the periodic system and the III-V compounds. All data were compiled from information on about 2500 pages in various volumes of the New Series of Landolt-Bornstein. For each critically chosen data set and each figure the original literature is cited. In addition, tables of content refer to the handbooks the data were drawn from. Thus the presentation of data in this volume is of the same high quality standard as in the original evaluated data collections. We hope to meet the needs of the physical community with the volumes of the series "Data in Science and Technology", forming bridges between the laboratory and additional information sources in the libraries.