The miniature high-speed gas-bearing turbomachinery is one of the research focuses in the fields of energy and cryogenic engineering in recent years. In this article, a new miniature static gas-bearing expansion turbine with a shaft diameter of 6 mm, turbine impeller diameter of 9 mm, and designed rotational speed of 300 000 r/min was developed. The developed prototype of this miniature expansion turbine is comprehensively introduced and the structure characteristics are presented. Then the preliminary mechanical and thermodynamic performances for the developed prototype are experimentally measured. Research results show that this developed expansion turbine has some noticeable features, such as stable operation with small vibration. It can reach 15 per cent over-speed and provide a quick temperature drop. Experimental verification demonstrates that both mechanical and thermodynamic performances agree with expected requirements. Hence, a strong base has been established in China to further develop miniature high-speed gas-bearing expansion turbines.