In this paper we describe silicon nitride (Si3N4) ceramic-based microdiffusion combustors with a two-dimensional structure, which is potentially batch-producible by microelectromechanical systems machining technology such as deep reactive ion etching. Si3N4 ceramic structures were fabricated by the nitridation of a spark-plasma-sintered silicon green compact after mechanical micromilling. Five types of combustor with a combustion chamber volume of 181 μl and depths of 1, 2 and 3 mm were tested. The combustors with combustion chamber depths of 2 or 3 mm achieved stable combustion at equivalence ratios from 0.28 to 1.3 and total flow rates from 4.0 to 11.3 SLM. They formed a flame at the center of the combustion chamber as designed, when the equivalence ratio was low. However, the combustor with a combustion chamber depth of 1 mm could not maintain a flame in the combustion chamber. This may be because combustion was not completed due to the shallow combustion chamber with a depth equivalent to the quenching distance of hydrogen.