We present the fabrication of a microlens array which can be integrated into a microfluidic device. In the demonstrated technique, a microwell array is firstly fabricated in a Parylene-C layer by a standard cleanroom process. Afterwards, the optically transparent dielectric microspheres with high refractive index are patterned inside the well template by utilizing an electrostatic technique. The mechanism of microsphere patterning is studied, and the lens effect of the microsphere is experimentally verified in a water-based medium. We also present a detailed two-dimensional numerical optical simulation study on the patterned microspheres using the Finite Element Method (FEM).