We have studied the composition profiles of Stranski-Krastanov InAs/GaAs quantum dots grown on patterned nanohole arrays. Two dimensional surface chemical maps obtained by X-ray photoemission electron microscopy reveal a non-uniform composition profile similar to that of standard dots grown on planar surfaces, with an enhanced In concentration at the center of the islands, with respect to the wetting layer. A statistical analysis, however, revealed an improvement of about 50% of dot composition uniformity associated with the already reported enhancement of size uniformity. No significant size or composition variation was found by changing the period of the hole pattern from 250 to 600 nm. (C) 2010 Elsevier B.V. All rights reserved.