The structural stability of InAs stacking-fault tetrahedron (SFT) in InAs/GaAs (1 1 1) is theoretically investigated. Using an empirical interatomic potential, cohesive energies are calculated for the three types of InAs/GaAs(1 1 1) system where coherent InAs and relaxed InAs with the SFT and misfit dislocations (MDs). The calculated results reveal that InAs with the SFT is more favorable beyond the film thickness of 21 monolayers (MLs) than coherent InAs. The critical film thickness of 21 ML is comparable with that of 8 ML for the MDs generation. This suggests that the SFT appears in InAs thin film layers instead of MDs resulting from lowering the strain energy accumulated in InAs thin film layers. (c) 2007 Elsevier B.V. All rights reserved.