We present an AlGaN/GaN metal-insulator-semiconductor-heterostructure field effect transistor (MIS-HFET) with an $Al_2O_3-HfO_2$ laminated high-k dielectric, deposited by plasma enhanced atomic layer deposition (PEALD). Based on capacitance-voltage measurements, the dielectric constant of the deposited $Al_2O_3-HfO_2$ laminated layer was estimated to be as high as 15. The fabricated MIS-HFET with a gate length of 102 m exhibited a maximum drain current of 500 mA/mm and maximum tr-ansconductance of 125 mS/mm. The gate leakage current was at least 4 orders of magnitude lower than that of the reference HFET. The pulsed current-voltage curve revealed that the $Al_2O_3-HfO_2$ laminated dielectric effectively passivated the surface of the device.