It is demonstrated that hydrogenation induces microdefects and electronic deep levels in single-crystal silicon, which are unrelated to either plasma or radiation damage. After hydrogenation of either n-type or p-type silicon, transmission electron microscopy reveals defects that can be described as hydrogen-stabilized platelets or microcracks which appear within 0.1 1/4m of the exposed surface and are predominantly oriented along {111} crystallographic planes. These defects correlate with high concentrations of hydrogen or deuterium as measured by secondary-ion mass spectrometry and with the appearance of SiH bonds as revealed by Raman spectroscopy. The concomitant introduction of electrically active gap states is demonstrated with both photoluminescence spectroscopy (PL) and deep-level transient spectroscopy (DLTS). In PL several H-induced radiative transitions are observed, with the dominant peak at 0.98 eV, which had previously been ascribed to plasma damage. In n-type Schottky diodes, DLTS detects two H-induced levels with thermal activation energies for electron emission of approximately 0.06 and 0.51 eV. These defects are detected at depths greater than the surface layer, are in low concentrations (<1013 cm-3), are acceptorlike, and anneal with an activation energy of 1/40.3 eV. © 1987 The American Physical Society.