Differences have been found on the growth rate of epitaxial layers grown simultaneously on semi-insulating and P and N type (100) GaAs substrates from the same Ga As liquid solution. The layers were grown by LPE at 786degreesC using an initial supercooling of 15degreesC and a cooling rate of 0.5degreesC/min. The thickness of the grown layers was measured, under an optical microscope, in cleaved cross-sections etched in a FeCl3-HCl solution. To fit the thickness-growth time data to the theoretical expression used for diffusion-limited growth it is necessary to use different initial supercoolings for the layers grown in each substrate, in spite that those layers were grown at the same time, from the same solution and therefore under exactly the same conditions. (C) 2004 Elsevier B.V. All rights reserved.