We present the first search for bosonic superweakly interacting massive particles (super-WIMPs) as keV-scale dark matter candidates performed with the GERDA experiment. GERDA is a neutrinoless double-beta decay experiment which operates high-purity germanium detectors enriched in Ge-76 in an ultralow background environment at the Laboratori Nazionali del Gran Sasso (LNGS) of INFN in Italy. Searches were performed for pseudoscalar and vector particles in the mass region from 60 keV/c(2) to 1 MeV/c(2). No evidence for a dark matter signal was observed, and the most stringent constraints on the couplings of super-WIMPS with masses above 120 keV/c(2) have been set. As an example, at a mass of 150 keV/c(2) the most stringent direct limits on the dimensionless couplings of axionlike particles and dark photons to electrons of g(ae) < 3 x 10 -12 and alpha'/alpha < 6.5 x 10(-24) at 90% credible interval, respectively, were obtained.
