Nowadays, one of the appealing choice of transistors for the next generation of high power devices is, AlGaN/GaN high-electron-mobility transistor (AlGaN/GaN-HEMT). Prior to now, numerous experiments were conducted utilizing various gate engineering techniques to propose high threshold voltage enhancement-mode HEMT architectures. In this paper, two new e-mode HEMT structures are proposed by taking motivation from our previously reported structure of Recessed p-GaN gate HEMT. By incorporating p-doped buried layer with recessed p-GaN gate in one HEMT structure, the threshold voltage is significantly increased. In first experiment, a p-doped GaN region is buried in to the Gallium Nitride (GaN) substrate of conventional p-GaN gate HEMT. In second experiment, a p-GaN buried layer is inserted in to GaN substrate of recessed p-GaN gate HEMT. V _th of above 3V is obtained from the proposed structures, which is suitable to be implemented for high-frequency power switching applications. The proposed structures provides flexibility to tune V _th and I _d. The digital circuit compatibility is also tested by using both the proposed structures in a resistive-load inverter circuit. The transient analysis confirms that the HEMTs work properly in inverter circuit and the VTC analysis shows 98.5% of output voltage swing at input voltage of 5V. Highest NM _H and NM _L is measured as 2.85V and 2.65V respectively. The device simulation, calibration and circuit simulation is done in Silvaco TCAD software.