We report on the first observation of metastable defects in n-type silicon implanted with 90 keV hydrogen ions at 88 K at a dose of 2×1010 cm-2. Schottky contacts were fabricated on the implanted surfaces to study room-temperature stable defects by deep-level transient spectroscopy. After reverse-bias cooling, three new peaks (Ec–0.29, 0.41, 0.55 eV) appear in addition to well-known defects. Metastable defects are hydrogen-related and their production rates are higher in the 88 K implantation than in the room-temperature implantation.