Co-flowing laminar streams in microfluidic devices are used to create microsecond mixers, produce materials and guide light. These tools can benefit from the high-throughput, controlled nature of microfluidic systems by miniaturizing, scaling, and understanding co-flow. This has been addressed by designing a three-dimensional microfluidic device to actively miniaturize co-flowing streams to thicknesses of less than one micron. This architecture allowed for devices to scale both the size and number of co-flows. Up to 64 submicron streams were generated in a single microchannel. The quality of produced co-flows was investigated with respect to limitations of diffusion at low flow rates and Dean flow alterations at high flow rates.