The design, fabrication and characterization of liquid-filled microchannels embedded in silica layers and integrated with optical waveguides for applications in on-chip sensors and novel photonic devices are presented. These integrated microstructures are formed using plasma-enhanced chemical vapor deposition (PECVD), photolithography and reactive ion etching (RIE). Surface accessible fluid introduction ports have been developed, and microfluidic circuits including bends, T-junctions and splitters are demonstrated. Coupling of light from integrated solid silica waveguides via directional coupling or direct end-fire coupling into fluid filled channels has been achieved on-chip, and optical losses assessed experimentally and theoretically. Optimization of the microstructures for sensor applications and for novel photonic devices based on nonlinear and other optical properties of fluids in integrated liquid waveguide segments is discussed.