Abstract: The characterizaion of source-drain burnout of niicrowave GaAs power MESFET has been invesigated by means of Scannin Electron Microscope（SEM） and Scanning Auger Microprobe（SAM）.It is found by SEM that the surface micrograph of source-drain burnout is complex。 The surface micrograph of burnout shows difference,it is sericous in some regions, owever, it is less seri-ous in the teroh regions. The SAM results indicate that the Ohmic contact layers of source and drain completely disappear in the burnout regions. The microarea near the burnout regions it not destructed. There are elements C, O, Ti, N and Ga in the burnout region surfaces. Elements C and O distrlbutes in a certain of depth in the burnout region. Combining SEM with SAM resuls,the mecha-nism of the source-drain burnout is also discussed.