PURPOSE: To provide a titled device which enables the formation of a uniform and thick hot silicon nitride film by providing a hollow jig for decomposing a nitrogen compound between a material to be nitrided placed in a reaction tube and an ejection port for reactive gas.

CONSTITUTION: A material 11 to be nitrided such as a silicon wafer is placed on a susceptor 2, and is set in a reaction tube 31. The inside of the tube 31 is evacuated and NH3 is introduced therein to maintain the atmosphere contg. virtually neither oxygen nor water in the tube 31. The material 11, the susceptor 2 and a nitrogen compd. decomposing jig 8 are heated by a heater such as an IR lamp 71. The NH3 ejected from a gas introducing port 41 is decomposed on the surface of the jig 8. The decomposed nitridable material diffuses easily in the formed Si3N4 film and arrives at the boundary between the Si3N4 film and silicon thus forming the Si3N4 film by reacting with the silicon. The growth of the hot silicon nitride film is thus easily progressed.