Here we report the design, fabrication, and characterization of a lab-on-a-chip device using a nanotube-based sensor array. The microfluidic components are composed of an ultraviolet (UV) light-defined, cross-linked SU-8 microchannel and a polydimethylsiloxane (PDMS) top cover. The hybrid microfluidic structure provides a fully sealed microchannel, well-aligned features, and precisely positioned nanosensors. Well-organized single-walled carbon nanotube (SWNT) thin films are deposited and aligned across the electrodes on a silicon substrate with dielectrophoresis. The assembly of SWNTs is carried out in a sealed microchannel. The SWNT devices are configured as two-terminal resistor-type sensors with the metal electrodes as the probing pads and the dielectrophoretically captured SWNTs as the sensing elements. The SWNT devices are used as integrated flow sensors to monitor the flow rate in the microchannel. In addition, when exposed to aqueous solutions with various pH values, these sensors change their resistance accordingly and demonstrate high sensitivity towards pH solutions.