High　resistance　GaN　thin　film　was　grown　on　sapphire　(0001)　substrates　using　metal-organic　chemical　vapor　deposition　(MOCVD).　Effect　of　the　GaN　nucleation　layer　growth　parameters,　including　reactor　pressure,　species　of　carrier　gas　and　growth　time,　on　the　electrical　characteristics　of　the　following　grown　GaN　buffer　was　investigated.　It　is　found　that　GaN　films　epitaxially　grown　on　the　GaN　nucleation　layers　deposited　at　a　relatively　lower　pressure　tend　to　have　a　high　resistance.High　resistance　GaN　buffer　layer　can　also　be　prepared　by　extending　growth　time　of　the　nucleation　layer　(i.e.　increasing　the　thickness　of　nucleation　layer)　or　by　using　N2　instead　of　H2　as　carrier　gas　during　the　growth　of　nucleation　layer.　GaN　layers　with　a　sheet　resistance　as　high　as　2.49×1011　Ω/　was　obtained.　These　layers　were　used　as　templates　for　the　preparation　of　epi-wafers　with　AlGaN/AlN/GaN　hetero　structures,　which　were　used　to　fabricate　high　electron　mobility　transistors　(HEMTs).　The　highest　mobility　of　these　samples　reaches　to　1　230　cm2/(V·s).