A semiconductor device having a deposited phosphosilicate glass film, containing an insubstantial amount of hydrogen and a low phosphorus concentration, is manufactured at a high mass productivity. This semiconductor device is manufactured by first placing plural substrates for semiconductor devices to be treated in a reaction tube so that the main surfaces of the substrates are substantially vertically aligned with respect to one another and are substantially perpendicularly intersected by the central axis of the reaction tube, the reaction tube being provided with at least two gas feed pipes having plural small openings pierced along the longitudinal direction thereof. Second, a silicon compound gas is introduced through one of the gas feed pipes into the reaction tube and an oxidizing gas is introduced through the other of the gas feed pipes into the reaction tube, while the inside of the reaction tube is maintained a reduced low pressure, whereby phosphosilicate glass films are deposited on the main surfaces of the substrates.