Influence of reactor pressure on the quality of GaN layers grown by hydride vapor phase epitaxy (HVPE) has been studied. With the reactor pressure decreasing from 7 to 5 x 10(4) Pa, improvements in structural, optical, and electrical properties of the GaN films have been observed. An investigation of the surface morphology of the GaN films reveals that the improvements arise from the change of the growth mode from an island-like mode at high pressures to a step-flow one at low pressures. These results clearly indicate that the reactor pressure, similar to the growth temperature, is one of the important parameters to control the qualities of HVPE-GaN epilayers. (C) 2008 Elsevier B.V. All rights reserved.