This　study　presents　an　investigation　of　high-voltage　enhancement-mode　p-GaN　gate　HEMTs　on　a　sapphire　substrate.　The　breakdown　voltage　of　the　devices　shows　a　linear　relationship　with　the　LGD.　For　LGD=27　μm,　the　device　exhibits　a　high　breakdown　voltage　of　1412　V.　The　threshold　voltage　is　0.9　V.　The　Ron　is17.7\　Ωmm,　and　the　specific　on-resistance　Rsp　is　6.73　mΩcm2.　To　measure　the　depletion　region　directly　for　high-voltage　devices,　depletion-testing　structures　were　fabricated　alongside　the　HEMTs.　The　depletion　lengths　were　determined　based　on　the　I-V　characteristics　of　the　structures,　with　the　pinch-off　voltage　of　the　I-V　characteristics　correlated　to　the　depletion　length.　Additionally,　using　pulse　waveforms　as　the　gate　control　signals,　the　formation　of　the　depletion　region　under　dynamic　conditions　was　revealed.　©　2023　IEEE.