Abstract: A package for an optical semiconductor device includes an eyelet, a signal lead inserted in a through hole formed in the eyelet, and sealing glass sealing the signal lead in the through hole. The signal lead includes a first portion, a second portion and a third portion that are greater in diameter than the first portion and on opposite sides of the first portion, a first tapered portion extending from the second portion to the first portion, and a second tapered portion extending from the third portion to the first portion. The first portion and the first and second tapered portions are buried in the sealing glass. The total length of a part of the second portion in the sealing glass and a part of the third portion in the sealing glass is 0.2 mm or less.