A technique is developed to enable accurate layer thickness control and planarization in a multilayer SU-8 2000 micromachining process, while maintaining a high quality surface finish. Relying on carefully controlled mechanical lapping and polishing stages, layer thicknesses from 30–400 μm have been routinely achieved to an accuracy of ±3 μm with excellent planarity. High-aspect ratio structures (intended for use in a millimeter-wave engineering application) with up to five layers and of 770-μm thickness have been fabricated using this method. The quality of the resulting surfaces has been investigated and characterized using scanning probe microscopy: a typical rms surface roughness of around 10 nm has been measured. The problem of air-bubble formation and migration encountered during the lapping stage has been documented along with a technique for their elimination. It is also shown that the common problem of the expansion of the lower layers in a multilayer structure due to solvent reabsorption can be effectively eliminated through careful process optimization.