An electro-optical device having two wafer components and a device fabrication method. A first wafer component includes a silicon substrate and a cladding layer on top thereof. The cladding layer comprises a cavity formed therein, wherein the cavity is filled with an electrically insulating thermal spreader, which has a thermal conductivity larger than that of the cladding layer. The second wafer component comprises a stack of III-V semiconductor gain materials, designed for optical amplification of a given radiation. The second wafer component is bonded to the first wafer component, such that the stack of III-V semiconductor gain materials is in thermal communication with the thermal spreader. In addition, the thermal spreader has a refractive index that is lower than each of the refractive index of the silicon substrate and an average refractive index of the stack of III-V semiconductor gain materials for said given radiation.