A sample injection system and a capillary electrophoresis channel integrated,together on a planar glass substrate are described, and the performance is evaluated. Voltages of at least 25 kV may be applied over an 11-cm-long capillary channel with sufficient dissipation of the Joule heat generated (1.8 W/m). The glass substrate sustains at least 10 5 V/cm dc without dielectric breakdown. Using laser-induced fluorescence detection, mixtures of fluorescein derivatives and fluorescein isothiocyanate-labeled amino acids were injected and separated. Up to 100 000 theoretical plates and -20 plates/V were obtained under optimized conditions, comparable to results with fused-silica capillaries