[en] Highlights: • Sacrificial layer assisted microfabrication method was developed for CO₂ laser engraving. • Six thermoplastics were found compatible with sacrificial layer assisted laser engraving technique. • Microchannel width as small as ∼ 40 μm was attainable by a laser beam that was 5 times larger in diameter. • Inherent bulging issue of laser engraved microchannel has been solved such that good bonding quality can be achieved. - Abstract: Since polydimethylsiloxane (PDMS) is notorious for its severe sorption to biological compounds and even nanoparticles, thermoplastics become a promising substrate for microdevices. Although CO₂ laser engraving is an efficient method for thermoplastic device fabrication, it accompanies with poor bonding issues due to severe bulging and large feature size determined by the diameter of laser beam. In this study, a low-cost microfabrication method is proposed by reversibly sealing a 1 mm thick polymethylmethacrylate (PMMA) over an engraving substrate to reduce channel feature size and minimize bulges of laser engraved channels. PMMA, polycarbonate (PC), polystyrene (PS), perfluoroalkoxy alkane (PFA), cyclic-olefin polymers (COP) and polylactic acid (PLA) were found compatible with this sacrificial layer assisted laser engraving technique. Microchannel width as small as ∼40 μm was attainable by a laser beam that was 5 times larger in diameter. Bulging height was significantly reduced to less 5 μm for most substrates, which facilitated leak proof device bonding without channel deformation. Microdevices with high aspect ratio channels were prepared to demonstrate the applicability of this microfabrication method. We believe this fast and low-cost fabrication approach for thermoplastics will be of interest to researchers who have encountered problem with polydimethylsiloxane based microdevices in their applications.