Diamond junction field-effect transistors (JFETs) were operated in bipolar-mode to enhance the drain current. In unipolar-mode, the drain current in diamond JFET is limited by low activation of boron acceptors in the p-type channel. To increase the drain current, minority carriers were injected from the n+-diamond gates to p-channel, resulting in conductivity modulation. The drain current increased by a factor of up to 8.5 with current gains of 100–2600. We confirmed that the bipolarmode operation can be performed at a high temperature of 200 ºC. The combination of the bipolar-mode and high temperature operation will lead to the realization of low-loss diamond power devices.