PURPOSE: To obtain a photo semiconductor device of high photo coupling efficiency with a single mode fiber and small variation of the efficiency with the variation of ambient temperatures by a method wherein a hole is provided through a member for holding a lens, and a pin provided on a heat sink which holds a photo element is inserted into this hole and fixed.

CONSTITUTION: A plurality of holes are bored through the semi-circular metallic holding member 11, composed of Cu, etc., plated with Au of good wetting property with solder over the surface, the lower semisphere of a spherical lens 10 composed of high refractive index glass is fitted therein, and the lower side surface of the upper semisphere is fixed on the member 11 by means of a low melting point solder glass 12 whose main component is PbO. On the other hand, a semiconductor laser element 20 positioned at the lower surface of the lens 10 is mounted on the heat sink 30 via a member 21 such as a diamond of high thermal conductivity, and a plurality of projecting pins 31 provided in the sink 30 are fixed in another hole provided at the end part of the holding member 11 by means of Sn-Pb series solder 40. Thereafter, the entire surface is covered with a transparent glass surface plate 51, and the end part thereof is supported by a holding metal piece 50.