A pair of substrates each having a bonding surface are joined together by interposing a bond layer precursor coating between the bonding surfaces of the substrates and heating the precursor coating to form a bond layer. Prior to the joining step, the substrate on the bonding surface is provided with a gas-permeable layer. Even when a material which will evolve a noticeable volume of gas upon heat curing is used as the precursor coating, substrates can be joined via a robust bond without the peeling problem by gas evolution.