A hydrogenation method that utilizes plasma directly exposes a crystalline semiconductor film to the plasma, and therefore involves the problem that the crystalline semiconductor film is damaged by the ions generated simultaneously in the plasma. If a substrate is heated to 400.degree. C. or above to recover this damage, hydrogen is re-emitted from the crystalline semiconductor film. To solve these problems, a method of fabricating a semiconductor device according to the present invention comprises the steps of forming a hydrogen-containing first insulating film on a semiconductor layer formed into a "predetermined shape, conducting heat-treatment in a hydrogen atmosphere or in an atmosphere containing hydrogen formed by plasma generation, forming a second insulating film in contact with the first insulating film, conducting heat-treatment in a hydrogen atmosphere or in an atmosphere containing hydrogen formed by plasma generation, forming a hydrogen-containing third insulating film on the second insulating film and conducting heat-treatment in an atmosphere containing hydrogen or nitrogen.