Silicon piezoresistive pressure sensors can only operate below 125 °C due to the leakage current of the PN junction. However, silicon-on-insulator (SOI) high-temperature pressure sensors use SiO2 for total dielectric isolation to solve this problem. At present, SOI high-temperature pressure sensors mostly use lead bonding package structure, with gold wire to lead the electrical signal and silicone oil as the protection medium, but the working temperature of silicone oil is limited to about 150 °C. In this paper, the leadless package structure is designed using pressure conduction on the backside of the chip and replacing the gold wire with sintered silver paste. The materials and dimensions of the leadless package structure are determined and then obtained a complete package structure through manufacturing. The reliability of the leadless package structure after silver paste sintering was verified by finite element analysis, and the results showed that the thermal stress caused by high and low-temperature cycles in the leadless package is minimal and does not affect the sensitivity of the pressure-sensitive chip. The size of the leadless package structure was optimized by Taguchi orthogonal method, and the maximum thermal stress was effectively reduced. Also, the key factors affecting the thermal stress of the leadless package in the package structure were identified by the variance number analysis method. The optimized leadless package structure size was remanufactured, and the sintered package structure was tested. The data show that the sensitivity of the pressure sensor is 30.82 mV/MPa with a nonlinearity of less than 0.4% full-scale (FS).