There have been a very few reports on on-demand droplet spotter for functional solutions containing metal particles. Making use of its characteristics, we develop a new method of fabricating microstructures. In this process, microdroplets are formed on-demand by means of a high pulse voltage between the functional solution containing Fe_3O_4 particles in a glass capillary and a polydimethylsiloxane (PDMS) substrate; a two-dimensional microarray can thus be formed on the substrate. We investigate to obtain optimum experimental conditions or factors that give generation of a regular array of droplets. Further, we study, by an FEM simulation, the behavior of Fe_3O_4 particles and PDMS sheet when a magnetic field is applied to the two-dimensional array.