We have studied the effect of growth interruptions on 2 monolayer thick InAs/InP strained quantum wells (QWS) grown by chemical beam epitaxy. The main feature is the formation of up to 8 monolayer thick InAs islands during As, annealing of the QW. Their formation is characterized by a two- to three-dimensional transition of the reflection high energy electron diffraction (RHEED) pattern and by multiple-line photoluminescence spectra. This interpretation of the data is confirmed by transmission electron microscopy (TEM).