The present paper describes an emerging field, "Si microphotonics", and its application to on-chip interconnection beyond semiconductor roadmap. Current Si-LSIs have been facing three fundamental limits associated with metal interconnection; i.e., slow clock speed, multilayer interconnection for high density interconnects, and high power consumption. These limits are induced by "slow" signal messengers, electrons. There is no solution beyond the Cu and low k technology but optical interconnection. To implement optical clock distribution on a chip, one challenge is sharp bending of waveguides. High-index contrast optics has shown their significant potentials. Right angle bends have been proto-typed whose area is less than 1 tm2. Ge directly grown on Si wafers shows an excellent characteristics as photodetectors for 1.3 and 1 .55 tm. A high-density interconnection needs wavelength division multiplexing (WDM). Ultrasmall multiplexer/demultiplexer (DEMUX/DEMUX) has been achieved on a chip based on micro-ring resonators (1O tm). Minimization ofpower consumption is of importance when light sources are implemented on a chip. Microcavity resonators based on photonic crystal concepts should be a unique solution.