Abstract: Provided are a nitride-based high electron mobility transistor having enhanced frequency characteristics and an improved structural stability and manufacturing method thereof. The nitride-based high electron mobility transistor includes a first semiconductor layer and a second semiconductor layer sequentially formed on a substrate, source drain electrodes formed on the second semiconductor layer, a first insulating film formed on the second semiconductor layer and having an opening, a dielectric formed on the first insulating film to surround the opening of the first insulating film, a second insulating film formed on an inner sidewall of the dielectric, and a gate electrode formed on the dielectric to fill the opening of the first insulating film and inside the inner sidewall of the dielectric. A width of the inner sidewall at a bottom end of the dielectric is smaller than a width of the inner sidewall at a top end of the dielectric.