A method and apparatus that may be utilized for chemical vapor deposition and/or hydride vapor phase epitaxial (HVPE) deposition are provided. In one embodiment, a metal organic chemical vapor deposition (MOCVD) process is used to deposit a Group III-nitride film on a plurality of substrates. A Group III precursor, such as trimethyl gallium, trimethyl aluminum or trimethyl indium and a nitrogen-containing precursor, such as ammonia, are delivered to a plurality of straight channels which isolate the precursor gases. The precursor gases are injected into mixing channels where the gases are mixed before entering a processing volume containing the substrates. Heat exchanging channels are provided for temperature control of the mixing channels to prevent undesirable condensation and reaction of the precursors.