Magnetic head fabrication for >100 Gbit/in.(2) areal density requires minimum lithographic feature size <0.15 mum, with aspect ratios of 8:1-10:1. Electron-beam lithography can provide adequate resolution for research and development of magnetic heads, and at 100 kV can provide greater than 10:1 aspect ratios in 1-3 mum thick single-layer resist poly (methylmethacrylate). Poly (methylmethacrylate) (PMMA) is well known for withstanding the rigors of plating baths, but at these thicknesses requires a nonswelling, low-stress developer such as the LIGA mixture (also known as "GG Developer (U.S. Patent No. 4,393,129)."). In this work we present the results of isopropyl alcohol:water development for thick PMMA, and describe the dependence of resist contrast on the temperature of the developer. We also demonstrate the advantage of ultrasonic agitation during development. These development techniques have brought resist profiles in PMMA to the theoretical limit predicted by Monte Carlo simulations.