An integrated microchannel reactor and heat exchanger comprising: (a) a waveform sandwiched between opposing shim sheets and mounted to the shim sheets to form a series of microchannels, where each microchannel includes a pair of substantially straight side walls, and a top wall formed by at least one of the opposing shim sheets, and (b) a first set of microchannels in thermal communication with the waveform, where the waveform has an aspect ratio greater than two.