PURPOSE: To produce a well-sealed semiconductor device by a method wherein the brazing materials with specific melting point welded into cap and package for optical semiconductor device are welded into each other.

CONSTITUTION: A cap 11 for optical semiconductor device with a brazing material 10 with melting point not exceeding 200°C welded into sealing frame surface and a package 12 with another brazing material 17 with the same melting point not exceeding 200°C welded into the periphery of a cavity wherein an optical semiconductor device 18 is diemounted and wired are sealed with each other by means of welding said brazing materials 10 and 17 into each other. As for said brazing materials, solders with melting point of 100W200°C such as indium, indium tin alloy and indium tin etc. may be used. Besides, the optical semiconductor device element 18 is provided with a casein organic filter 20 on a silicon chip 19. When the cap 11 is fixed by pressure to the package 12 containing the optical semiconductor device element 18 with the organic filter 20 in the atmosphere of inert gas at the temperature of 150W200°C wherein the solder with lower melting point may be fusion-welded, the organic filter 20 may be sealed airtightly suffering no damage at all.