A microreactor includes a shell structure (2, 3), having a bottom wall (2) and a peripheral wall (3); a layer (5), accommodated in the shell structure (2, 3) and having cavities (9, 10) formed therein, the cavities being accessible form outside the shell structure (2, 3); reagents (17), arranged between the bottom wall (2) and the layer (5), at locations corresponding to the cavities (9, 10). The layer (5) is made of a meltable material that is solid at room temperature, has a melting point (TMP) lower than a maximum operative temperature (TMAX) required by reactions performable through the microreactor (1) and is not miscible with water. The melting point (TMP) may be between 50° C. and 70° C. In one embodiment, the melting point (TMP) is lower than a minimum operative temperature (TMIN) required by reactions performable through the microreactor (1).