Spontaneous formation of self-assembled InAs quantum dots (QDs) is strongly influenced by growth parameter-dependent intermixing of the deposit with substrate material. This paper describes an analytical approach to model InAs QD formation that in particular considers intermixing. Intermixing is modelled based on thermally activated vertical exchange processes where Ga atoms from the GaAs substrate transmit the wetting layer via a two-step process. With the model, the intermixing-induced QD composition as well as the critical coverage of QD formation is calculated. Calculated values of the critical coverage at various growth parameters are found to agree well with our experimental electron diffraction data. In particular, the calculation results exhibit a flux-dependent critical temperature limiting QD formation that is found in experiments as well. (c) 2006 Elsevier B.V. All rights reserved.