Novel methods and apparatuses for annealing semiconductor devices in a high pressure gas environment. According to an embodiment, the annealing vessel has a dual chamber structure, and potentially toxic, flammable, or otherwise reactive gas is confined in an inner chamber which is protected by pressures of inert gas contained in the outer chamber. The incoming gas delivery system and exhaust gas venting system are likewise protected by various methods. Embodiments of the present invention can be used, for example, for high-K gate dielectric anneal, post metallization sintering anneal, and forming gas anneal in the semiconductor manufacturing process.