The influence of backside illumination and temperature on the fabrication of large and high aspect ratio silicon microchannel plates (MCPs) by photoelectrochemical (PEC) process is described. Backside illumination is provided by three tungsten halogen lamps with a feedback loop, keeping a constant current density. The etching temperature is maintained by a circulation system. Proper backside illumination and the lower temperature can provide better integrated etching conditions compared to that without illumination and temperature control. Etching under the improved conditions results in smoother undercutting and better surface topography for large (effective diameter of about for silicon substrates) silicon microchannel plates. Enhancing the backside illumination within the etching temperature range ensures that the aspect ratio is more than 40, boding well for applications of silicon microchannel plates.