Hiatus semilunaris is present in

Middle meatus: Uncinate process is a hook-like structure running in from anterosuperior to the posteroinferior direction in the middle meatus. It&;s postero superior border is sharp and runs parallel to the anterior border of bulla ethmoidalis. This gap between the two is called hiatus semilunaris .it is two-dimensional space of 1-2 mm width. (Ref: Diseases of Ear, Nose and Throat and head and neck surgery, Dhingra 7th edition, Pg no. 150)