To compare the annealing effects on GaMnAs-doped with Zn (GaMnAs: Zn) and undoped GaMnAs ( u-GaMnAs) epilayers, we grew GaMnAs thin films at 200 degrees C by molecular beam epitaxy (MBE) on GaAs substrates, and they were annealed at temperatures ranging from 220 degrees C to 380 degrees C for 100 min in air. These epilayers were characterized by high-resolution X-ray diffraction (XRD), electrical, and magnetic measurements. A maximum resistivity at temperatures T-m close to the Curie temperatures T-c was observed from the measurement of the temperature-dependent resistivity rho(T) for both the GaMnAs: Zn and the u-GaMnAs samples. We found, however, that the maximum temperature Tm observed for GaMnAs: Zn epilayers increased with increasing annealing temperature, which was different from the result with the u-GaMnAs epilayers. The formation of GaAs: Zn and MnAs or Mn-Zn-As complexes with increasing annealing temperature is most likely responsible for the differences in appearance. (C) 2008 Published by Elsevier B. V.