The present invention provides a receiving optical subassembly (ROSA) with a co-axial shape and a stem for mounting semiconductor devices thereon that improves the high frequency performance of the ROSA. The ROSA mounts a photodiode (PD) and a pre-amplifier on a stem and the stem has a hollow the PD and the pre-amplifier are mounted therein. Since the hollow has a depth substantially equal to a thickness of the pre-amplifier, the bonding wire from the pre-amplifier to the surface of the stem may become shortest to reduce the parasitic inductance of the bonding wire and to enhance the high frequency performance of the ROSA.