Two methods are currently used for heating substrates in metal-organic chemical vapor deposition (MOCVD): rf heating and quartz lamp heating. This paper reports a new method, the quartz-envelope heater, and describes its use for producing undoped GaAs with AsH₃ and TMG in an MOCVD system. Also discussed are growth-rate and morphological studies, variations of electrical properties with different growth parameters, and refinements to the present heater design.