A new embossing method based on sacrificial templates and fast surface heating was developed, in which the de-embossing step was avoided to prevent deformation or damage of polymer microstructures. The microstructures of interest have a high feature density, high aspect ratio, and/or undercuts. Soft lithography was used to prepare a water-soluble mold, using polyvinylpyrrolidone (PVP) in the hot embossing process. Arrays of microchannels and microgrids with an aspect ratio greater than five were replicated on poly(DL-lactide-co-glycolide) (PLGA). In conjunction with localized surface heating of the polymer surface by a laser/IR system, this technique was able to micromold high temperature polymers such as poly(methyl methacrylate) (PMMA) with high aspect ratios.