PURPOSE: To form a passivation film not affected by humidity by allowing an exposed insulating layer in a semiconductor device to react with the gas of hexamethyldisilazane or trimethylchlorosilane.

CONSTITUTION: An N layer 10a and a P+ layer (a light-receiving layer) 10b and a P layer guard ring 10c are shaped into a Ge substrate 10, and a Ge photo- detector 20, to which a passivation film 11 composed of SiO2, an antireflection film 12 consisting of SiO2 and an electrode 13 is formed, is constituted onto these layers and guard ring. A hexamethyldisilazane liquid 16 is introduced into a vessel 15 in a closed vessel 14, and volatilized. Hexamethyldisilazane reacts with SiO2 as the passivation film, introduces CH3 groups to the uppermost surface of SiO2, is changed into hydrophobic properties, and does not react with moisture in air. Trimethylchlorosilane also displays an effect of improving the moisture resistance of the passivation film similarly.