Substrates for microchannel plates have been fabricated using Si micromachining techniques. High aspect ratio pores are constructed using reactive ion etching and streaming electron cyclotron resonance etching, and low-pressure chemical vapor deposition (LPCVD). In one process, 40 mu m deep pores with 2 mu m openings on 4 mu m centers are directly etched in Si. Alternatively, pores with aspect ratios of 30:1 are constructed in a low-stress SiNx membrane using a sacrificial template process whereby pillars of Si are etched and then subsequently backfilled with a dielectric using LPCVD.