An optical semiconductor module according to the embodiment includes: a board including a transmission line; a block including a low-permittivity material; an inductor mounted on the block, the inductor being connected with the transmission line via a first wire, the first wire having a first inductance; a semiconductor laser device mounted on the board, the semiconductor laser device being connected with the transmission line via a second wire, the second wire having a second inductance smaller than the first inductance; and
a housing configured to accommodate the board, the block, the inductor, and the semiconductor laser device.