In this paper, we present a fabrication method that is capable of making three dimensional (3D) microfluidic devices with multiple layers of homogeneous polystyrene (PS) film. PS film was chosen as primary device material due to its advantageous features for microfluidics applications. Thermopress is used as bonding method because it provides sufficient bonding strength while requires no heterogeneous bonding materials. By aligning and sequentially stacking multiple layers (3 to 20) of patterned PS film which were achieved by a craft cutter, complicated 3D structured microfluidic devices can be fabricated by multiple steps of thermopress bonding. The smallest feature can be achieved in this method is around 100 μm, which is limited by the resolution of the cutter (25μm) as well as the thickness of the PS films.Bonding characteristics of PS films are given in this paper, including PS film bonding strength test, bonding precision assessment, and PS surface wettability manipulation. To demonstrate the capability of this method, the design, fabrication and testing results of a 3D interacting L-shaped passive mixer are presented in the paper.