The present invention discloses a vacuum gauge of the Pirani type for measuring the pressure of vaporized organic or inorganic material used in forming a layer of a device, comprising: an extended filament having a thickness of 5 microns or less and having a temperature coefficient of resistance greater than 0.0035/ DEG C., the filament being subject to the vaporized organic or inorganic material; means for applying a current to the filament so that the temperature of the filament is less than 650 DEG C. so as not to degrade the molecular structure of the organic material; and a structure responsive to a change in resistance or a change in current to determine heat loss from the filament, which is a function of the pressure of the vaporized organic or inorganic material.