We investigated temperature dependence of the photoluminescence (PL) efficiency of GaN/Al0.08Ga0.92N multi-quantum wells (MQWs) with variations of Si-doping condition and threading dislocation density. Si-doping in the GaN/Al0.08Ga0.92N MQWs, especially in the barrier layer improves the PL efficiency. In addition, reduction of threading dislocation density also improves the PL intensity. The PL intensity of the GaN/Al0.08Ga0.92N MQW is drastically increased at least by a factor of 40, by a combination of the Si-doping and reduction of threading dislocation density. We fabricated a light emitting diode (LED) emitting at 357 nm using such a GaN/Al0.08Ga0.92N MQWs. Electro-luminescence intensity from the region with threading dislocation density of less than 108 cm−2 was much larger than that from the region with threading dislocation density of 6×109 cm−2.