A substrate assembly for supporting an optical component includes a substrate having a front surface and a first recess, a second recess formed portion disposed in the first recess and having a second recess smaller in diameter than the first recess and having an open end at least at a side corresponding to the front surface, the second recess formed portion being made of a material having a machinability better than a material forming the substrate, and an alignment guide member fitted in the second recess and having a protruded portion protruding from the front surface of the ceramic substrate and fittingly engageable in an alignment hole of the optical component. A method of producing such a substrate assembly is also provided.