Microchannels having highly enhanced surface area have been fabricated by a thin-film deposition technique known as glancing angle deposition. Porosimetry and simulation of the microstructures was used to estimate the surface area enhancement of the new microchannels. Two distinct types of microchannels have been created. In the first, a pre-existing microchannel is coated with a film of SiO2 deposited at a highly oblique angle. The resulting structure consists of the original channel Filled with slanted columns of SiO2. An example of this type of channel was estimated by porosimetry to have surface area of 517 cm(2)/cm(2). The second microchannel type is produced by lithographic methods and consists of films of SiO2 with helical microstructure bounded by walls of photoresist. Simulation of one example of this type of channel led to an estimate of 42 cm(2)/cm. This estimate, however, ignores the mesoscopic scale surface roughness of the microstructures.