PURPOSE: To prevent the permeation of moisture by providing a step part on the side of a lead for suspending a tab of the pellet fitting part of a lead frame.

CONSTITUTION: The tab 18 for fitting a pellet is supported monolithically on the lead side by the lead 16, while the thickness of the tab 18 and a heat-radiating piece 22 is larger than those of the lead 16 for suspension, an inner lead 14 and an outer lead 10. The taper part of the tab 18 for preventing slip-off is crushed 24, 26 by a mold to improve its adhesiveness to resin, while a groove 28 is formed thereon to prevent the permeation of moisture from the side of the heat-radiating piece 22. Moreover, a thin-plate-shaped part 30 is formed at the end surface on the lead side of the tab 18 by machining when the lead frame is punched out, and by a step part thus formed the permeation of moisture from the side of the lead 16 is prevented. A device sealed 34 with resin, which is prepared by using the lead frame having such a constitution, shows excellent wetproof property.