ZnO layer in a role of passivation of the AlGaN/GaN-based high electron mobility transistors (HEMTs) is presented. The thin layer is deposited by pulsed laser deposition technique. It is fully compatible with the process technology of high electron mobility transistors prepared on AlGaN/GaN heterostructures due to its physical properties similar to the GaN. We have succeeded to (1) suppress the gate leakage current; (2) increase the maximum of the drain current and the electron drift mobility, and (3) ensure the threshold voltage to be unaltered by employment of the thin ZnO layer to the channel area of the HEMT.