The exchange biasing properties of MnO/GaMnAs have been investigated by Eid et al. in detail by varying annealing condition. Moreover, a promising antiferromagnetic material IrMn has been identified due to its high exchange bias energy (Jk), high blocking temperature (Tb), and low critical thickness (~70 Å). The present work is a comparative study of exchange biasing of GaMnAs/IrMn heterostructures. Ga0.95Mn0.05As (30 nm) epilayers were grown by MBE system on semi-insulator GaAs (001) substrates. Then, the samples were transferred to another ultra high vacuum chamber to deposit the overgrown layers IrMn (10 nm)/Ta (5 nm) by dc magnetron sputtering system. In order to set up good exchange bias and decrease structural defects, the samples were annealed at temperature range from 150 to 200oC in a 1300 Oe field for 30 minutes. For as-prepared sample the magnetization curves show symmetric with respect to zero field, indicating absence of exchange bias. Moreover, the exchange bias effect was enhanced and demonstrated for GaMnAs/IrMn heterostructures after anneal procedure. Furthermore, the sample shows atomically flat with a root mean square (rms) roughness ~0.3 nm by atomic force microscopy (AFM). In spite of these new works, the origin of exchange bias with thermal treatment is not yet fully understood. Auger electron spectroscopy (AES) and Secondary Ion Mass Spectrometer (SIMS) analysis were carried out in order to study the extent of GaMnAs/IrMn interdiffusion during the thermal treatment. Furthermore, more magnetic characterization and detailed microstructures were performed and discussed by SQUID magnetometer and HRTEM analysis, respectively.