BaZn2As2 is expected for a good p-type semiconductor and has two crystalline phases of an orthorhombic alpha phase and a higher-symmetry tetragonal beta phase. Here, we report that high-quality epitaxial films of the tetragonal beta-BaZn2As2 were grown on single-crystal MgO (001) substrates by a reactive solid-phase epitaxy technique. Out-of-plane and in-plane epitaxial relationships between the film and the substrate were BaZn2As2 (001)//MgO (001) and BaZn2As2 [200]//MgO [200], respectively. The full-widths at halfmaximumwere 0.082 degrees for a 008 out-of- plane rocking curve and 0.342 degrees for a 200 in-plane rocking curve. A step-and-terrace structure was observed by atomic force microscopy. The band gap of beta-BaZn2As2 was evaluated to be around 0.2 eV, which is much smaller than that of a family compound LaZnOAs (1.5 eV). Density functional theory calculation using the Heyd-Scuseria-Ernzerhof hybrid functionals supports the small band gap. (C) 2013 Elsevier B. V. All rights reserved.