Weinvestigateeffectsofannealingonmagneticpropertiesofathick(Ga,Mn)Aslayer,andfindadramaticincreaseoftheCurietemperaturefrom65to115Kbypostgrowthannealingfora500-nm(Ga,Mn)Aslayer.AugerelectronspectroscopymeasurementssuggestthattheincreaseoftheCurietemperatureismainlyduetodiffusionofMninterstitialtothefreesurface.Thedouble-crystalx-raydiffractionpatternsshowthatthelatticeconstantof(Ga,Mn)Asdecreaseswithincreasingannealingtemperature.Asaresult,theannealinginducedreductionofthelatticeconstantismainlyattributedtoremovalofMninterstitial.