An　ultraviolet　photodetectors　with　p-i-n　structure　based　on　GaN　by　RMBE　method　growing　on　sapphire　are　introduced,　and　the　measurement　of　their　electronic　characteristics　is　presented.　The　result　is:　Vth　approximately　equals　4.6　V,　Vbr　greater　than　or　equal　40　V,　the　dark　current　is　6.68　pA,　and　the　peak　responsivity　is　0.115　A/W　at　367　nm　while　the　reverse　voltage　is　3　V.　The　peak　responsivity　is　6.59　×　10-5A/W　at　400　nm,　which　is　four　orders　of　magnitude　lower　than　peak　responsivity.