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The InGaN/GaN multiple quantum wells are grown on a (0001)-oriented sapphire by using metalorganic chemical vapor deposition. Dependences of the photoluminescence (PL) peak energy and PL efficiency on injected carrier density and temperature are studied. The results show that the temperature-dependent behavior of the peak energy is in the manner of decrease-increase-decrease (S-shaped), and the maximum of the PL efficiency is observed at about 50 K. The former is attributed to the potential inhomogeneity and local characteristics of the carrier recombination in the InGaN matrix. The latter indicates that the traditional method that the internal quantum efficiency (IQE) is considered to be 100% at low temperature, should be corrected. Furthermore, it is found that the IQE depends on not only temperature but also injected carrier density. Based on the above discussion, an improved method of setting the IQE, i.e., measuring the dependence of PL efficiency is proposed.