Hydrogen (H) implantation-induced damage was investigated in (100) germanium (Ge) for the physical understanding of the surface blistering phenomenon. Ge samples were implanted at liquid nitrogen and room temperatures using 100 keV H+ ions with a fluence of 1 x 10(17) cm(-2). The hydrogen ion current density was kept at 10 A mu A cm(-2) during the implantation. H-implanted samples were subsequently annealed at higher temperatures up to 500 A degrees C in order to trigger surface blistering. X-ray diffraction studies of the H-implanted samples showed the existence of damage-induced stress and its prominent dependence on the implantation temperature. Damage-induced stress was found to be sufficiently large to guide the hydrogen diffusion and defects agglomeration. Microstructural investigations of the H-induced damage were carried out using cross-sectional transmission electron microscopy and annular dark-field scanning transmission electron microscopy. It showed that H-induced agglomerated defects were in the form of platelets surrounded by the strain field. Strain field strains the matrix lattice for the eventual occurrence of surface blistering in H-implanted Ge.