In this paper, high-efficiency STPV systems are investigated using spectrally selective absorber/emitter consisted of metal-dielectric multilayer and a GaSb TPV cell. A solar-thermophotovoltaic (STPV) system is expected to as highefficiency solar energy conversion using single-junction photovoltaic (PV) cells. However, the reached experimental system efficiency has been still low because spectral control of emitter is not sufficient. Narrowband thermal radiation from the emitter is effective for obtaining high-efficiency STPV systems, exceeding the Shockley-Queisser limit. From theoretical analysis, the narrowband thermal emitter can leads to obtain PV conversion efficiency over 45% at Qvalue= 30 and 1300K. The spectrally selective absorber/emitter was also investigated to obtain high ηPV. The ηPV = 23.5% was estimated by the fabricated emitter spectrum, which exceeds the Shockley-Queisser limit of 19.6% for a GaSb bandgap of 0.67 eV. The entire STPV system and the power generation tests were conducted using the fabricated absorber/emitter. The total system efficiency 4.9% at 1505K was obtained under an irradiance of 109 Wcm-2.