Features and analysis modes of secondary ion mass spectrometry (SIMS) as applied to elemental and compound semiconductors are reviewed. Semiconductor materials are described. The SIMS technique and what it can do are analyzed by examining separately the ion beam, sputtering, the surface, mass analysis, and the secondary ions. Secondary ion enhancement, sputtering rates, impurity - matrix interactions, machine parameters, signal detection modes and dynamic range, depth profile scale calibration, detection sensitivity and depth profile aberrations are discussed. The applications of bulk analysis, imaging, mass scanning, and depth profiling are described. Special capabilities like high mass resolution are pointed out.