This paper suggests miniature silicon flow paths for a miniature organic Rankine cycle (ORC) generator that utilizes waste heat. Conventionally, most waste heat energy in an industrial plant is lower than 573 K. This waste heat energy can serve as a renewable power source for IoT devices by realizing a miniature organic Rankine cycle generator. To build such a miniature generator, miniature flow paths that connect the structural parts were developed. The developed flow paths were fabricated using a microelectromechanical systems (MEMS) process, and a plate type and a multilayer type were designed. The dimensions of the plate type flow path were 50 mm (length) by 50 mm (width), creating a flow path area 1.75 mm wide and 0.3 mm deep. The multilayer type was a three-dimensional structure measuring 10 mm (length) by 6.0 mm (width) by 3.7 mm (height), with a path width of 1.05 mm. A low-boiling-point working fluid (boiling point of 307 K) was injected into these structures to reuse waste heat energy. The plate type flow path showed displacement of the working fluid by a phase change when the heating temperature was 310 K and the cooling temperature was 282 K. In the multilayer type flow path, the working fluid was discharged by expanding the fluid at 308 K and 313 K. In addition, the outflow pressure (needed to embed this structure into a miniature ORC system in the future) was calculated. The developed structure achieved an outflow differential pressure of 2.2 kPa when the heating temperature was 313 K and the cooling temperature was 293 K. These results show that the developed MEMS flow paths realized the displacement and heat transport of the working fluid by phase change.