Temperature-dependent photoluminescence (PL) of phase-separated InGaN quantum wells is investigated over a broader excitation power range. With increasing excitation power from 0.5 μW to 50 mW, the In-rich quasi-quantum dot (QD)-related PL peak disappears at about 3 mW, while temperature behavior of the InGaN matrix-related PL peak energy (linewidth) gradually evolves from a strong “S-shaped” (“W-shaped”) temperature dependence into a weak “S-shaped” (an approximately “V-shaped”), until becoming an inverted “V-shaped” (a monotonically increasing) temperature dependence. This indicates that, with increasing excitation power, the carrier localization effect is gradually reduced and the QD-related transition is submerged by the significantly enhanced InGaN matrix-related transition, while the carrier thermalization effect gradually increases to become predominant at high excitation powers.