High-efficiency Mn4+-activated red phosphor of K2SiF6:Mn4+ synthesized at low temperature was utilized to fabricate phosphor-converted white light-emitting diodes (pc-WLEDs). Temperature-dependent electroluminescence (EL) measurements were undertaken at a constant forward voltage mode. A large negative-thermal-quenching (NTQ) effect is demonstrated for the luminescence intensity of this kind of red phosphor in the temperature range of 100-300 K. It is found that its enhancement rate is several times higher than those of the blue chip and the green component, such that the overall color of the pc-WLED shows a wide color gamut in the studied temperature range. By utilizing this outstanding NTQ property of the red phosphor, a color rendering index up to R a=93 is obtained for the high-brightness pc-WLED with relatively low blue light from the LED chip.