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The results of research into Surface Acoustic Wave -SAW -devices have been recognized for their efficiency and versatility in the electrical signals processing [1], [3]. Actual progress in the industrial application of piezoelectric materials such as Lithium Niobate (LiNbO 3 ), Langasite (LGS), Lanthanum-Gallium Silicate La 3 Ga 5 SiO 14 and Gallium Orthophosphate (GaPO 4 ), allows the manufacturing of devices with performances, which overcome the limits obtained with quartz crystals [2]. The single crystal materials have a long term high stability -near to infinite -and moreover, some of these have an excellent behavior with temperature variation, as is the case of GaPO 4 [4]. Today, GaPO 4 with its properties is by far the best suited piezoelectric material to be used in sensor applications for machine monitoring and pressure measurements, at high temperatures. SAW microdevices based on GaPO 4 operate at temperatures of up to 800 0 C. We have developed five SAW filters based on GaPO 4 . The paper describes the steps to solve the problems regarding the use of GaPO 4 substrates for the development of SAW filters. In the 3rd chapter of the paper are given some experimental results obtained with Network Analyzer.

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