We have investigated the formation of InAs quantum dots grown by molecular beam epitaxy on GaAs substrates with different orientations using photoluminescence spectroscopy in pulsed magnetic fields (< 50 T). On increasing the amount of InAs deposited on (1 0 0)-oriented GaAs to 1.6 monolayer (ML), an abrupt change from one-dimensional to three-dimensional charge confinement is observed. For substrates cleaved along the (3 1 1)B plane, the charge confinement is found to be much weaker and gradually increases with the amount of InAs. At the highest coverage studied (1.9 ML), the quantum-dot confinement is equally effective for both substrate orientations. (C) 2002 Elsevier Science B.V. All rights reserved.