Ga melts were heated in a boron nitride crucible at 800 degrees C and 5 MPa of N-2 for 8-200 h with Na vapor. Colorless and transparent prismatic GaN single crystals grew from a Na-Ga melt which was formed by dissolution of Na from the gas phase. Nitrogen was probably introduced into the melt with Na. The time dependence of the Na fraction (rNa = Na/(Na + Ga)) in the melts and the yields of GaN were investigated. rNa increased to 0.39-0.43 within 100 h, and then became almost constant at this value. The yield of GaN was less than 2% at 50h. The yield increased linearly with heating time after 75h, and reached 57% at 200h. GaN single crystals with a size of 1.5 mm long were obtained on the bottom of the crucible wall. The largest crystals (3.0 mm-long and 1.2 mm-wide) grew at the edges of the melt and of the GaN crystal formation area near the bottom wall of the crucible. (c) 2005 Elsevier B.V. All rights reserved.