Abstract: A substrate processing apparatus configured to from a layer on a plurality of substrates is disclosed. Embodiments of the presently described substrate processing apparatus comprise a process chamber. The process chamber comprises process space for receiving a substrate boat arranged for holding the plurality of substrates. The substrate processing apparatus further comprise a gas delivery assembly comprising at least one gas injector; a gas exhaust assembly comprising two gas outlets. The two gas outlets are positioned at a distance on either side of the at least one gas injector.