A gain-clamped semiconductor optical amplifier comprises: at least one first surface; at least one second surface, each second surface facing and electrically isolated from a respective first surface; a plurality of nanowires connecting each opposing pair of the first and second surfaces in a bridging configuration; and a signal waveguide overlapping the nanowires such that an optical signal traveling along the signal waveguide is amplified by energy provided by electrical excitation of the nanowires.