Deep x-ray lithography is a fabrication method for the production of microstructures with aspect ratios of up to 100 in up to several millimeter thick resist layers. Usually, poly (methylmethacrylate) is used as the resist layer. We have measured the molecular weight and developing rates of crosslinked and noncrosslinked PMMA foils at different GG developer temperatures fdr dose values between 0.1 and 8 kJ/cm(3). The determined developing rates cover a region of 7 orders of magnitude: With decreasing temperature the contrast of the resist-developer system and the Limit of the developing dose are increased, Crosslinked PMMA has a higher contrast compared to noncrosslinked material. These effects lead to an enhanced quality of microstructures, which is demonstrated by the grating of the LIGA microspectrometer.