Using deep level transient spectroscopy (DLTS) measurements with zero-bias and reverse-bias cooling, we have observed new metastable defects (EM1, EM2 and EM3) in n-type silicon by hydrogen implantation at temperature as low as 88 K. We have investigated the trap parameters of these metastable defects and their concentration depth profiles. Hydrogen ion implantation was performed with energies of 80 keV, 90 keV, and 100 keV to a dose of 2 × 1010 cm−2. The silicon substrate temperature was kept at as low as 88 K during hydrogen implantation and then was raised naturally to room temperature. From analysis of Arrhenius plots, the energy levels of EM1, EM2 and EM3 are obtained to be Ec-0.29 eV, Ec-0.41 eV and Ec-0.55 eV, respectively. The depth profiles of metastable defects in 90-keV samples have a peak in the concentration around the depth of 0.68 µm, which is shallow compared with the projected range of 90 keV hydrogen. The peak position becomes deeper as the energy of ion implantation increases. This indicates that the production of metastable defects is caused by ion implantation. Additionally, comparison with helium-implanted samples suggests that implanted hydrogen is included in these metastable defects.