This work presents the implementation of a thick SU-8 layer as a mask in the microabrasive jet machining (μ-AJM) process. A microchannel with an aspect ratio of 0.33, which was obtained in this work, had an arc-shape with a width of 190 μm and a depth of 70 μm. The process phenomena that are important for achieving a qualified microchannel for microfluidic applications are discussed. By using the repeated sequence of steps proposed in this paper, three-dimensional microchannels on a single glass slide can be fabricated.