In　this　paper,　the　AlGaN/GaN　HEMT　(high　electron　mobility　transistors)　with　different　ohmic　contact　structures　are　fabricated,　and　the　effect　of　different　ohmic　contact　pattern　on　GaN　HEMT　electrical　properties　is　studied.　A　conventional　ohmic　contact　electrode　structure　and　a　new　ohmic　contact　structure　with　a　contact　hole　are　fabricated　and　subjected　to　rapid　thermal　annealing　(RTA)　in　flowing　N-2.　After　different　structured　AlGaN/GaN　HEMTs　are　annealed　at　750　degrees　C　for　30　seconds,　in　HEMTs　with　a　conventional　structure　ohmic　contact　still　does　not　form　while　in　the　device　with　ohmic　contact　holes　a　good　ohmic　contact　is　already　formed.　Then　the　surface　morphology　of　different　multilayer　electrode　structures　is　measured.　Comparing　Ti/Al/Ti/Au　with　Ti/Al/Ni/Au,　we　can　conclude　that　the　structure　Ti/Al/Ni/Au　has　a　more　smooth　surface　after　annealing.　After　testing　the　HEMT　devices　with　different　structures,　higher　transconductance　and　saturation　current　are　found　for　the　devices　with　ohmic　contact　holes.　But　a　serious　current　collapse　phenomenon　has　been　observed　when　the　gate　voltage　is　set　between　0.5　V　and　2　V.