We present a new class of periodic dielectric structures designed spec
ifically to be amenable for fabrication at submicron lengthscales. The
structures give rise to a sizable 3D photonic band gap and can be fab
ricated with materials widely used today in optoelectronic devices. Th
ey are made of three materials and consist essentially of a layered st
ructure in which a series of cylindrical air holes are etched at norma
l incidence through the top surface of the structure. Our results demo
nstrate the existence of a gap as large as 14% of the midgap frequency
using Si, SiO2, and air; and 23% using Si and air.