Based on the hydrogen-terminated surface channel diamond material,a 1μm gate length diamond metal-insulator-semiconductor field-effect transistor(MISFET) was fabricated.The gate dielectric Al_2O_3 was formed by naturally oxidated thin Al metal layer,and a less than 2 pA gate leakage current was obtained at gate bias between -4 V and 4 V.The DC characteristic of the diamond MISFET showed a drain-current density of 80 mA/mm at drain voltage of -5 V,and a maximum transconductance of 22 mS/mm at gate-source voltage of -3 V.With the small signal measurement,a current gain cutoff frequency of 2.1 GHz was also obtained. Based on the hydrogen-terminated surface channel diamond material, a 1 μm gate length diamond metal-insulator-semiconductor field-effect transistor (MISFET) was fabricated. The gate dielectric Al 2 O 3 was formed by naturally oxidized thin Al metal layer, and a less than 2 pA gate leakage current was obtained at gate bias between -4 V and 4 V. DC characteristic of the diamond MISFET showed a drain-current density of 80 mA / mm at drain voltage of -5 V, and a maximum transconductance of 22 mS / mm at gate-source voltage of -3 V.With the small signal measurement, a current gain cutoff frequency of 2.1 GHz was also obtained.