The first stainless-steel microchannel (MC) emulsification chips with grooved MC arrays, each consisting of uniform-sized parallel channels and a terrace, were developed. These chips enabled successful spontaneous-transformation-based generation of uniformly sized droplets of soybean oil and silicone oil. As for the influence of the dispersed-phase velocity in a channel, the critical velocity below which uniform-sized droplets were obtained from the channels depended on the interfacial tension between two phases. The maximum productivity of uniform-sized oil droplets for the stainless-steel MC emulsification chips was estimated to be several milliliters per hour. An adapted capillary number that considers the wettability of the dispersed phase of two different oils could be useful for understanding the flow state of the dispersed phase during droplet generation.