We, present a one-step technology for fabrication of Topas-based lab-on-a-chip (LOC) microsysterris by the use of thermal nanoimprint lithography (NIL). The technology is demonstrated by the fabrication of two working devices: a particle separator and a LOC with integrated optics for absorbance measurements. These applications demonstrate the fabrication of millimeter to micrometer-sized structures in one lithographic step. The use of NIL makes the technology easily scalable into the nanometer regime by the use of a suitable lithographic technique in the fabrication of the stamp. Processing issues such as environmental stress cracking of the Topas and the requirements to anti-sticking layers on the stamp when imprinting into Topas are discussed. (c) 200.5 American Vacuum Society.