We present the epitaxial growth and processing as well as measurement results of vertical-cavity surface-emitting lasers (VCSELs) monolithically integrated with photodiodes for high-speed bidirectional data transmission over multimode fibers. For this purpose, metal-semiconductor-metal and PIN photodiodes have been investigated. Reflectivity measurements of the as-grown structure reveal the expected emission wavelength of the laser buried underneath the photodiode layers. Digital data transmission up to 6 Gbit/s is demonstrated. (C) 2010 Elsevier B.V. All rights reserved.