A description is given of the fabrication and analysis of thin phase holograms in several photoresist systems. The dependence of hologram efficiency, in the electromagnetic domain, on groove shape and groove depth will be demonstrated. Control of these parameters is crucial and depends largely on thorough characterization of the photoresist. Of particular importance is the relationship between Remaining Resist Thickness and Exposure Energy for a specific set of processing conditions. From this data, modulation depths for different exposure levels can be predicted. Distinctly different groove profiles can be realized on the same resist by varying processing parameters. Scanning electron micrographs of highly efficient rectangular and sinusoidal profiles are shown. Experimentally established relationships between efficiency and modulation ratio (groove depth/groove spacing) are compared with recently published diffraction theory for transmission, dielectric surface relief gratings.