Concentration and thermal release of hydrogen in hydrogenated amorphous SiC (a-SiC:H) films were studied. The films were prepared onto Si (111) wafers at room temperature by rf planer magnetron sputtering in a gas mixture of argon at partial pressures of 0.33 Pa and hydrogen from 0.065 to 1.3 Pa. The LR measurements conducted on the films annealed at various temperatures for 3600 s suggested that the hydrogen was released from Si-H and C-H bonds in the films at the temperatures above 600 and 850 K, respectively. In-situ isochronal annealing for 300 s at various temperatures from 323 to 1123 K in the ERDA (Elastic Recoil Detection Analysis) system was carried out for the specimen having the hydrogen concentration of 7.1 X 10(27) atoms/m(3). It was revealed that three types of hydrogen exist in the films; hydrogen bonded to Si or C atoms and unbonded hydrogen, with the concentrations of 2.8 X 10(27), 1.9 X 10(27) and 2.4 X 10(27) atoms/m(3), respectively. The concentration of unbonded hydrogen decreases with increase of the hydrogen partial pressure.