Fischer-Tropsch synthesis (FTS) involves highly exothermic conversion of syngas to a wide range of hydrocarbons, but demands isothermal conditions due to the strong dependence of product distribution on temperature. Running FTS in microchannel reactors is promising, as the sub-millimeter dimensions can lead to significant intensification that inherently favors robust temperature control. This study involves computer-based FTS simulations in a heat-exchange integrated microchannel network composed of horizontal groups of square-shaped cooling and wall-coated, catalytic reaction channels. Effects of material type and thickness of the wall separating the channels, side length of the cooling channel, coolant flow rate, and channel wall texture on reaction temperature are investigated. Use of thicker walls with high thermal conductivities and micro-baffles on the catalytic reaction channel wall favor near-isothermal conditions. Response of reaction temperature against coolant flow rate is significant. Using cooling channels with smaller side lengths, however, is shown to be insufficient for temperature control. (C) 2011 American Institute of Chemical Engineers AIChE J, 58: 227-235, 2012