PHOTONIC crystals are artificial structures having a periodic dielectric structure designed to influence the behaviour of photons in much the same way that the crystal structure of a semiconductor affects the properties of electrons(1). In particular, photonic crystals forbid propagation of photons having a certain range of energies (known as a photonic bandgap), a property that could be incorporated in the design of novel optoelectronic devices(2). Following the demonstration of a material with a full photonic bandgap at microwave frequencies(3), there has been considerable progress in the fabrication of three-dimensional photonic crystals with operational wavelengths as short as 1.5 mu m (ref. 4), although the optical properties of such structures are still far from ideal(5). Here we show that, by restricting the geometry of the photonic crystal to two dimensions (in a waveguide configuration), structures with polarization-sensitive photonic bandgaps at still lower wavelengths (in the range 800-900 nm) can be readily fabricated. Our approach should permit the straightforward integration of photonic-bandgap structures with other optical and optoelectronic devices.