High density patterns of holes in metalorganic chemical vapor deposition grown GaN films on sapphire have been fabricated by inductively coupled plasma etching using a nickel mask. Pattern transfer from the e-beam lithographically patterned resist to the nickel etch mask was accomplished by ion beam milling. A Cl-2-BCl3 inductively coupled plasma was used to anisotropically etch patterns of 200-250-nm-diam holes with 300 nm center-to-center spacing through the entire thickness of a 265-nm- and a 300-nm-thick GaN film. This work demonstrates a pattern transfer technique to Ni by ion beam milling and Ni as a durable etch mask under a chlorine environment for high density patterning of GaN films.