NOVELTY - Making a high aspect ratio compact chemical reactor (10) by creating at least two low aspect ratio process layers, forming low aspect ratio perimeter barrier(s), creating low aspect ratio cavities, repeating first to the third steps to create additional intermediate assemblies with low aspect ratio cavity or cavities, creating high aspect ratio cavities, repeating steps fourth and fifth steps to create a joined intermediate assemblies to create a compact chemical reactor with high aspect ratio cavities, and joining the compact chemical reactor.    USE - For use in manufacturing fuel cell layers.    ADVANTAGE - The invention is capable of manufacturing low cost chemical reactor. It provides high surface area process layers in connection with the reactant plenums through the front or back cavities.    DETAILED DESCRIPTION - Making a high aspect ratio compact chemical reactor with high aspect ratio cavities using components with low aspect ratio cavities comprises creating at least two low aspect ratio process layers, forming low aspect ratio perimeter barrier(s) by forming a barrier material into barrier shape(s), creating low aspect ratio cavities by joining the low aspect ratio perimeter barrier to side(s) of one of the low aspect ratio process layers creating an intermediate assembly with low aspect ratio cavity or cavities, repeating first to the third steps to create additional intermediate assemblies with low aspect ratio cavity or cavities, creating high aspect ratio cavities by joining one of the low aspect ratio process layers to the low aspect ratio cavities, repeating steps fourth and fifth steps to create a joined intermediate assemblies to create a compact chemical reactor with high aspect ratio cavities, and joining the compact chemical reactor with high aspect ratio cavities to two reactant plenums to facilitate a transport process between the reactant plenums and the process layers.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of compact chemical reactor.    Compact reactor (10)    Unit reactors (12, 16, 18, 20, 22, 24, 26, 28, 30, 31)    Front side (32)    Back side (34)    Reactant plenum (36)