PURPOSE:To seal a slag without using a positioning fixture by directly fixing the slag to the end section of a lead frame and fastening a glass sleeve and a semiconductor pellet, employing the slag as a support member. CONSTITUTION:Slags 11 are welded to the upper surfaces of each lead body 10a in a lead frame 10. The slags 11 are covered with glass sleeves 12, and semiconductor pellets 13 are inserted into the sleeves 12. Slags 15 are welded to the lower surfaces of each lead body l4a in a lead frame 14. The flames 10 and 14 are superposed under the state in which the slags 15 are faced oppositely to the upper surfaces of the sleeves 12, and the slags 15 are inserted into the sleeves 12. The frames are introduced into a heating furnace, the sleeves 12 are melted, and the outer circumferential surfaces of the slags 11 and the slags 15 and the inner circumferential surfaces of the sleeves 12 are sealed. Lastly, the frames 10, 14 are detached from an intermediate being taken out from the heating furnace. According to said method, the slags can be sealed without using a positioning jig.