Inverted 45° semiconductor mirrors as vertical optical couplers for PIC chips, particularly optical receivers and transmitters. An inverted 45° semiconductor mirror functions to couple light between a plane in the PIC chip defined by thin film layers and a direction normal to a top surface of the PIC chip where it may be generated or collected by an off-chip component, such as a wire terminal. In an exemplary embodiment, a (110) plane of a cubic crystalline semiconductor may provide a 45° facet inverted relative to a (100) surface of the semiconductor from which light is to be emitted. In further embodiments, a (110) plane may be exposed by undercutting a device layer of a semiconductor on insulator (SOI) substrate. Alternatively, a pre-etched substrate surface may be bonded to a handling wafer, thinned, and then utilized for PIC waveguide formation.