A thorough structural study has been performed on a series of MBE-grown NiMnSb/GaAs(0 0 1) films using Mn-55 and Sb-121(123) nuclear magnetic resonance. In addition to a small amount (<4%) of classical point defects, the films reveal some twinning faults leading locally to formulation of hexagonal MnSb. In case of stoichiometric NiMnSb, the amount of MnSb phase is estimated to be about 14% of a total sample volume. The excess of Sb increases the amount of MnSb environments, while in the Sb poor samples these inclusions practically disappear. (C) 2002 Elsevier Science B.V. All rights reserved.