The invention relates to a gas flowmeter capable of reducing a secular change comprises a silicon semiconductor substrate (2) formed with a cavity (9) and a heat element (4) formed above the cavity (9) of the semiconductor substrate (2) by way of an insulating film. The heat element (4) is a silicon (Si) semiconductor thin film impurity-doped at high concentration. Stoichiometrically stable silicon nitride (Si 3 N 4 ) thin films as barrier layers which less permeate and less absorb hydrogen in the heat generating temperature range of the heat element (4) are formed above and below the silicon (Si) semiconductor thin film.
