Abstract: A three-dimensional microstructure includes a plurality of structure elements, each structure element having a width, a length and a height, wherein a significant proportion of the structure elements have height dimensions which exceed their width and length dimensions. A method of fabricating such a microstructure includes the steps of: forming a mask with a plurality of regions, each region having a predetermined degree of transparency to UV radiation; providing a substrate (5) coated with a thick layer (6) of UV resist material; using UV radiation to irradiate through each of the regions of the mask a corresponding region of the layer of UV resist; and developing the layer of UV resist to remove irradiated regions, wherein the depth of each region is dependent upon the degree of transparency of the corresponding region of the mask.