Vertical Cavity Surface Emitting Laser (VCSEL) on silicon substrate. One embodiment described herein includes an apparatus with functionality for communicating optical signals on a silicon integrated circuit chip. The apparatus includes a silicon based integrated circuit chip die. An optical waveguide is formed at the silicon based integrated circuit chip die. A vertical cavity surface emitting laser (VCSEL) is mechanically coupled to the silicon base integrated circuit chip die and optically coupled to the optical waveguide.