Ceramic microchannel heat-exchanger and reactor technology is capable of achieving high performance while operating under high-temperature, corrosive, and/or oxidative environments. This work describes two computational fluid dynamics (CFD) modeling studies which examine the coupling of heat transfer and endothermic methane-steam-reforming chemistry within a ceramic microchannel reactor. These modeling tools are then applied to improve microchannel-reactor design and performance. Within the reactor, methane is converted to syngas through steam reforming; the thermal requirements for this endothermic chemistry are provided by heat transfer from hot-inert gas on adjacent layers. Fluid flow, heat transfer, and complex elementary surface chemistry are all simulated using the ANSYS FLUENT models. CFD studies reveal the substantial chemical contribution of reforming on thermal gradients across and within the reactor. Improved control of the reforming temperature is also discovered through stack-design analysis, where an odd number of inert-gas layers are found to create more-uniform reactive wall temperatures. Model results provide insight on the interplay of conjugate heat transfer and chemical kinetics in reactor design.