Abstract: Ohtnic contact is a ftindamental comoonent for GaAs devices and the performance of GaAs devices is strongly influenced by the electrical properties of the contact.A variety of metallization system for Ohmic con-tact has been developed and AuGeNi system is widely used.AuGeNi contact to n-GaAs With Si heavy doped prepared by RTP has been in Vestigated by AES in tbis paper. After con1paring the electrical properties and interfacial microstructures with different anncaling tempratures, the relation between microstructure and contact resistance has been discussed.A ideal interfacial microstructure for low contact resistance was developed,which would be helpful for process parafneters selecting.