A monolithic optoelectronic device has a spot-size converter optically connected to a waveguide. The overclad extending over the core of the waveguide is thinner and differently doped than the overclad of the spot-size converter. This structure can be made by applying a process of etching and enhanced selective area regrowth to create regions of the overclad of different thickness or doping. The spot-size converter core is made of a different material than the waveguide core by using etching and enhanced selective area regrowth.