Ferromagnetic MnAs layers with abrupt interfaces were grown by MBE on (001) and (311)A oriented GaAs substrates. At low growth rates and As-rich conditions, the films are ((1) over bar 1 0 0) oriented on both templates. For MnAs/GaAs(0 0 1) layers it is demonstrated that realizing a well-ordered reconstructed growth surface and the layer-by-layer growth mode on a thin MnAs buffer, films of high structural quality and very promising magnetic properties are obtained. The quality of thick films is limited by processes accompanying the beta --> alpha MnAs phase transition during sample cooling. The magnetic domains, their increase in size with increasing external magnetic field and their relation to topographical defects was studied by magnetic force microscopy combined with atomic force microscopy.