In the present work we have investigated the initial stage of InAs layer grown on porous GaAs (pi-GaAs) substrate by using reflection high-energy electron diffraction (RHEED) and low temperature photoluminescence (PL). RHEED measurements show that the 2D-3D growth mode transition appears after a deposition of 4.2 atomic monolayer (ML) of InAs, which is higher than that deposited on nominal GaAs (1.7 NIL). PL investigations show two luminescence bands at 1.24 and 1.38 eV. The 1.24 eV PL peak emission is associated to the radiative transitions in InAs quantum dots (QDs), whereas the 1.38 eV PL peak emission is attributed to the InAs wetting layer (WL). The results show that pi-GaAs is a promising candidate to obtain a reduced QDs size distribution, and to grow pseudomorphic epitaxial layer on GaAs substrate with higher indium concentration. (C) 2003 Elsevier B.V. All rights reserved.