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This paper reports the application of selective parylene C deposition for the waterproof coating of underwater shear-stress sensors. The selective deposition has been achieved by electrically heating the sensing element during deposition, utilizing the dependence of parylene deposition rate on substrate temperature. The electrical power supplied was only 20 mW to raise the temperature of the sensing element 210/spl deg/C above ambient due to the sensor's excellent thermal isolation. After selective parylene deposition, the sensing element was still exposed while other areas were covered by parylene. More effective interaction between the sensor and water was realized. With selective parylene deposition, excellent waterproof and high shear-stress sensitivity can be achieved at the same time.