This paper presents the novel fabrication of highly sensitive ionic liquid-based pressure sensor integrated in a poly(dimethylsiloxane) microfluidic device. The proposed fabrication method provides an ability to simultaneous fabrication of the pressure sensor and microfluidic components by multilayer soft lithography. To improve the sensitivity in a low-pressure range, sensor structure and electrical output are investigated by a numerical simulation. Then the analyzed sensor structure is precisely fabricated by three-dimensional (3D) lithography utilizing a numerical process optimization. Both numerical and experimental results revealed the sensor output depends on a cross section geometry of ionic liquid-filled channel, and confirmed the improved sensitivity.