A Metalorganic chemical vapor phase epitaxy or vapor phase deposition apparatus, having a first gas source system, a reactor, an exhaust gas system, and a control unit, wherein the first gas source system has a carrier gas source, a bubbler with an organometallic starting compound, and a first supply section leading to the reactor either directly or through a first control valve, the carrier gas source is connected to an inlet of the bubbler through a first mass flow controller by a second supply section, an outlet of the bubbler is connected to the first supply section, and the carrier gas source is connected to the first supply section through a second mass flow controller by a third supply section, the first supply section is connected to an inlet of the reactor through a third mass flow controller.