A microfabricated gas flow structure includes an array of vertical gas flow channels in a side-by-side parallel flow arrangement. Adjacent gas flow channels are separated by a thin wall having a thickness which can be an order of magnitude or more less than the channel width, offering exceptionally high area efficiency for the array. Channel walls can be formed from a dielectric material to provide the walls with sufficient integrity at nanoscale thicknesses and to provide thermal insulative properties in the lateral direction, thereby controlling power losses when the gas flow structure is employed as a Knudsen pump. The gas flow structure can be microfabricated as a monolithic structure from an SOI wafer, with the gas flow channels formed in the device layer and the heat sink formed from the handle layer.