GaN/GaP short-period superlattices were grown on GaP(111)A substrates by gas source molecular-beam epitaxy. Despite the large lattice-mismatch between GaN and GaP, reflection high-energy electron diffraction patterns showed the quick switch from GaN (GaP) streaks to GaP (GaN) streaks just after the corresponding switch of the growth. This indicates two-dimensional layer-by-layer growth resulting from the relaxation of lattice strain at the initial stage of the hetero-epitaxy. This phenomenon is considered to be due to the use of (111)A-oriented substrates. Bulk GaN layers were also grown on GaP(111)A substrates and the flat-surface GaN layers were obtained because of the two-dimensional layer-by-layer growth starting from the interface between GaN and GaP (111)A substrates. Strong near-band-edge photoluminescence with very weak deep-level emission was observed. GaP(111)A substrate is considered to be promising for the growth of GaN. (C) 2002 Elsevier Science B.V. All rights reserved.